Fisheries and Aquaculture

A DISTANCE COURSE MODULE ON

Fisheries and Aquaculture (Biol 421)

For Biology Students in Summer In-Service Program

By Mulugeta Wakjira (M.Sc.) Department of Biology Jimma University

Editor Tadesse Habtamu (M.Sc.) Department of Biology Jimma University

© CDE, Jimma University, Ethiopia

June, 2011 Jimma, Ethiopia

Table of Contents Table of Contents ..................................................... ..................................................................................................... ................................................ i

Module Introduction ........................................................ ............................................................................................ .................................... iii iii Chapter 1 Diversity of Fishes ............................................................................... 1

1.1. Diversity by Taxonomic Groups ............................................................................ 2 1.2. Diversity by Size, Habitat Type and Age .......................................................... 10 1.3. Diversity by Sexuality and Brooding Behaviour .......................................... 11 1.4. Diversity by Feeding Behaviour ......................................................................... 12 .............................................. 14 Chapter 2 Fish Reproduction and Development ..............................................

2.1. Fish Reproduction .................................................................................................... 15 2.1.1. Patterns of Sexuality in Fishes ......................................................... 15 2.1.2. Sites of Embryo Development in Fishes .......................................... 16 2.1.3. Fertilization and Spawning in Fishes ............................................... 17 2.1.4. Reproduction in Cartilaginous Vs Bony Fishes ............................... 22 2.2. Fish Growth, Development and Recruitment ................................................ 23 Chapter 3 Capture Fisheries .............................................................................. 27

3.1. Introduction................................................................................................................ 28 3.2. Fishing Gears and Crafts ........................................................................................ 32 3.3. Fishing Methods ........................................................................................................ 38 3.4. Commercially Important Fishes ......................................................................... 43 Chapter 4 Aquaculture ....................................................................................... 46

4.1. Introduction................................................................................................................ 47 4.2. Types of Aquaculture .............................................................................................. 49 4.3. Aquaculture Systems .............................................................................................. 54 4.4. Establishment of Aquaculture ............................................................................. 57 4.5. Sustainability of Aquaculture .............................................................................. 61 Chapter 5 Status and Prospects of Capture Fisheries and Aquaculture ........ 65

5.1. World Case .................................................................................................................. 66 5.2. Ethiopian Case ........................................................................................................... 69 Chapter 6 Benefits of Fisheries .......................................................................... 77 Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page i

6.1. Nutrition and Socio-economic Benefits .......................................................... 78 6.1.1. Subsistence or Artisanal Fishing ...................................................... 78 6.1.2. Industrial and Recreational Fishing ................................................. 83 Chapter 7 Processing and Products of Fish ...................................................... 85

7.1. Fish Processing Methods ....................................................................................... 86 7.1.1. Post-mortem Changes and Fish Quality .......................................... 86 7.1.2. Processing Methods .......................................................................... 92 7.2. Types of Fish Products ........................................................................................... 98 Chapter 8 Fisheries Management .................................................................... .................................................................... 100

8.1. Stock Assessment ................................................................................................... 101 8.1.1. Definitions and Stock Concept ....................................................... 101 8.1.2. Survey of Stock Population P opulation............................................................. 103 8.1.3. Quantitative Estimation of Stock Population ................................ 106 8.2. Sustainable Exploitation of Fisheries Resources .................. ..................... .......... ........... 108 Chapter 9 Fish Parasites and Diseases ............................................................ 114

9.1. Fish Immunity .......................................................................................................... 115 9.2. Major Fish Parasites .............................................................................................. 116 9.2.1. Protozoan Parasites of Fishes ....................................................... 119 9.2.2. Helminthic Parasites of Fishes ....................................................... 122 9.2.3. Copepod Parasites of Fishes ........................................................... 138 9.3. Major Fish Diseases ............................................................................................... 140 9.3.1. Bacterial Diseases of Fishes ............................................................ 140 9.3.2. Viral Diseases of Fishes ................................................................... 144 9.3. 3. Fungal (Mycotic) Diseases of Fishes ............................................. 146 References .......................................................................................................... 148 Appendix 1: Data on the status of world fisheries production by FAO (2000Table1), FAO (2008-Table 2) and FAO (2010-Table3). ................................. 151 Appendix 2: Assignment Questions ................................................................. 154

Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page ii

Module Introduction Dear student, this course (Biol 421) follows the Aquatic Sciences and Wetland Management (Biol 302) course. Therefore, it is necessary that you recall your past knowledge of the course Biol 302 for better understanding of the present course.

The course Fisheries and Aquaculture (Biol 421) introduces you to basic ideas and concepts in fisheries and aquaculture. Much emphasis has not been given to and only basic concepts have been addressed on fish biology due to credit hour constraint. Much emphasis has been given to the fisheries and aquaculture. A student taking this course is, thus, required to refer to chapter 6 of the course Aquatic Sciences and Wetland Management (Biol 302) besides what is given in this module on aspects of fish biology.

The present module has been organized into nine chapters. The first and second chapters deal with the diversity and reproduction of fish respectively. respectively. These two chapters appear to provide you with some basic concepts on the diversity and reproductive biology of fishes so that you would better understand the subsequent chapters. Chapters three and four discuss about the various aspects of capture fisheries and aquaculture, the two broad categories of fisheries practices. The chapters give distinctions between the two forms of fisheries and other underlying fundamental concepts. Chapter 5 addresses the status and prospects of capture fisheries and aquaculture on a global and national (Ethiopian) scale. Here various limitations associated with capture fisheries and aquaculture, and thus the prospect of both sectors has been discussed.


Page iii

In chapters six and seven the benefits of fisheries and the methods of processing fish products have been discussed respectively. Chapter six has incorporated points on the various socio-economic benefits generated by human being from the fisheries resources. Chapter seven discusses the various methods employed to process fish and fish products given the easily perishable nature of fish.

Chapter eight deals with fisheries management where the concept of sustainable exploitation of fisheries resources and related issues are raised. In the last chapter fish parasites and diseases that are important especially in aquaculture practices, and thus are of major socio-economic concern, have been widely addressed.

Moreover, presentation of the module is in such a way that "guiding questions” are frequently posed at intervals so that a student can understand and learn the concepts easily. Moreover, at the end of each chapter come questions related to the chapter and course or module objectives. Thus, after completing every chapter the student should test him/herself of the mastery of the chapter by answering all the questions.

Finally, an assignment comprising of various items form the whole chapters has been attached as Appendix 2 at the end of the module. Dear student, you are thus expected to copy all the questions down on a separate sheet of paper, work out all the questions and submit it to your course instructor upon completion of the course. The assignment constitutes a minimum of 25 % of your total marks.


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Course or Module Objectives Upon successfully completing this course, you will be able to: 

Discuss the diversity of fishes



Discuss the various modes mo des of sexuality and reproductive behaviours in fishes.



Distinguish between capture fisheries and aquaculture



Discuss the status and potential of fisheries and aquaculture both on the global and Ethiopian scale



Discuss the various socio-economic benefits of fisheries to human being especially in relation to ensuring food security for the needy community.



Mention and discuss the various fish processing and preservation methods



Explain the idea of fisheries management management



Identify and discuss the important fish parasites and diseases


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Diversity of Fishes Chapter Outline 1.1. Diversity by Taxonomic Groups 1.2. Diversity by Size, Habitat Type and Age 1.3. Diversity by Sexuality and Brooding Behaviour 1.4. Diversity by Feeding Behaviour

Chapter Objectives Upon completing this chapter, you will be able to: 

Discuss the characteristics of a typical fish



Discuss the various fish characteristics that make them more diverse than any of the vertebrate groups



Distinguish among the various classes of fishes



List down the major characteristics of the various fish classes



Distinguish between the extinct and extant fish groups



Distinguish among the types of aquatic environments inhabited by the various groups of fishes



Discuss habitat diversity of fish



Discuss the size diversity of fish



Discuss diversity of fishes in their feeding behavior



Discuss the diversity of fishes in their reproductive behavior behavior


Page 1

Fishes are very diverse and are categorized in many ways. For instance, fishes are diverse with respect to species number, body sizes, habitat type, age, sexuality, brooding behavior, feeding behavior, locomotion, toxicity, vulnerability, etc. We will discuss some of these fish diversities as shown above in the chapter outline.

1.1. Diversity by Taxonomic Groups

Activity:

Dear student, as an introduction to this chapter, from your knowledge of Aquatic Sciences and Wetlands Management (Biol 302) course module, chapter 6, would you please mention some of the characteristic features of a typical fish? A typical fish: 

is ectothermic (i.e. has variable body temperature)



has a streamlined body for rapid swimming



extracts oxygen from water using gills



has two sets of paired fins, usually one or two (rarely three) dorsal fins, an anal fin and a tail fin



has jaws



has skin that is usually covered with scales



is oviparous i.e. lays eggs.

However, it is important to note that there are many groups of fishes which are exceptions to these characteristics. For instance, •

Lungfishes have lungs to breathe atmospheric air

•

Lamprey and hagfish do not have the paired (i.e. pelvic and pectoral) fins

•

Lamprey and hagfish do not have jaws


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•

Some fishes are either viviparous or ovoviviparous i.e. give birth to live young.

Fish exhibit greater species diversity than any other class of vertebrates. For instance, according to FishBase about 31,900 species have been discovered and described by the year 2010. This makes fish to be more diverse than the combined total of the rest of vertebrates such as amphibians, reptiles, birds and mammals.

Activity:

Dear student, before we continue with our discussion of fish species diversity, can you explain what a FishBase is?

FishBase is a database or information system with key data on major biological characteristics of fishes such as reproduction, reproduction, ecology, feeding, etc. It was developed in 1989 and funded by the European Eu ropean Commission (EC) until 2000 when a consortium of various organizations took over the responsibility. You can access FishBase on the Internet at its website: www.fishbase.org

Activity:

Dear student, in the hierarchical classification of organisms, how many classes of fishes can be recognized? Early fish taxonomic classifications may treat all fishes as monophyletic group belonging to a single class namely “Class Fish”. Recent studies, however, revealed that fishes are rather diverse and paraphyletic i.e. fishes are collections of various groups such as ostracoderms, cyclostomes, placodermi,

acanthodi,

chondrichthyes

(cartilaginous

fishes)

and

osteichthyes (bony fishes) that are categorized into different classes.


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Therefore, we may rather recognize the taxonomic classification of fishes into 11 classes as summarised in Table 1.1 though this too may not be absolutely authoritative. All fishes, however, belong to Kingdom: Animalia, Phylum: Chordata, and Subphylum: Vertebrata.

Table 1.1. Classes of Fishes

S. No.

Class

Status

1

Pteraspidomorphi Pteraspidomorphi

Extinct

2

Anaspida

Extinct

Collectively

3

Conodonta

Extinct

known as

4

Cephalaspidomorphi Cephalaspidomorphi

Extinct

Ostracoderms

5

Thelodonti

Extinct

6

Myxini

Extant

(commonly hagfish) 7

Pteromyzontia

Placodermi

Jaw condition

Agnathan

(jawless) fishes

Collectively Extant

known as Cyclostomes

(commonly lampreys)

8

Remark

Extinct

Commonly called armoured fishes

9

Acanthodii

Extinct

Commonly called spiny sharks

10

Chondrichthyes

Extant

Gnathostoman

Commonly called (Jawed) fishes cartilaginous fishes

11

Osteichthyes

Extant

Commonly called bony fishes


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Agnathan Fishes

Activity:

Dear student, let’s now come to a brief discussion of agnathan fishes and then proceed to that of the gnathostoman fishes. Q1. Which of the agnathan fish classes are extinct (i.e. already disappeared) and which are still extant (i.e. living)? Q2. What are the major distinguishing characteristics of agnathan fishes?

Dear student, as you can see from Table 1.1, ostracoderms are entirely extinct while cyclostomes are the extant group of agnathan fishes. Agnathan fishes are generally primitive group characterized by: •

Lack of jaws and the paired (i.e. pelvic and pectoral) fins which are characteristic of more advanced fishes.

•

Possession of notochord instead of vertebral column.

Activity:

Dear student, why do you think that cyclostomes are named so?

The term “cyclostome” has been derived from two words “cyclo” meaning circular; and “stome” meaning mouth opening. Therefore, the group has been named so because of its possession of a roughly circular mouth by its members. Dear student, please refer to the Figures given in chapter 6 of your Aquatic Sciences and Wetlands Management course module to observe the circular mouth of agnathan fishes.


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Activity:

Dear student, from your knowledge of Aquatic sciences and wetland management course, can you give the two typical examples of cyclostomes with their feeding habits and habitats they occupy?

Dear student, the two typical examples of cyclostome fishes with their feeding habits and habitats they occupy are given in Table 1.2.

Table 1.2. Comparison of the two living groups of agnathan fishes.

Lamprey

Feeding habit

Hagfish

Suck blood from their hosts; Scavengers they are parasitic on other larger and advanced fishes

Habitat

Both freshwater and marine

Marine

Gnathostoman Fishes

Dear student, let us now come to the discussion of gnathostoman fishes. Activity:

Q1. How do gnathostoman fishes differ from the t he agnathan fishes? Q2. What are the four major groups or classes of gnathostoman fishes? The gnathostoman fishes are generally advanced group over the agnathan fishes. Unlike the agnathan fishes, these fishes possess paired fins and other characteristics of fish. The four groups or classes of gnathostoman fishes are Placodermi, Acanthodi, Chondrichthyes and Osteichthyes. As you can see from Table 1.1, Placodermi and Acanthodi are extinct whereas Chondrichthyes and


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Osteichthyes are extant groups. Placodermi is assumed to be the first vertebrate group to develop jaws and paired fins. In evolution it is also assumed that a branch of placodermi probably gave rise to the two main modern classes of fish: the Chondrichthyes and Osteichthyes. Chondrichthyes

Activity:

Dear student, Q1. What are the major characteristics of chondrichthyes? Q2. What kind of habitat d o they occupy? Q3. What are their major subgroups?

Chondrichthyes are commonly known as cartilaginous fishes due to their possession of an endoskeleton made up of cartilage. Moreover, they are characterized by their lack of swim bladders, different tail fin construction, lack of a gill covering (operculum), and a skin covered with tooth-like structures called denticles or placoid scales giving them a rough sandpaper appearance. appearance. They are almost exclusively marine in distribution. The cartilaginous fishes include two major subgroups: Elasmobranch or Selaschii (e.g. sharks, rays and skates) and Holocephalans (e.g. chimaeras

or ratfish). Osteichthyes

Activity:

Q1. How do osteichthyes differ from the cartilaginous fishes? Q2. What are the major subgroups of osteichthyes?


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Osteichthyes are commonly known as bony fishes because of their possession of bony endoskeleton as opposed to the cartilaginous fishes. Moreover, they differ from the cartilaginous fishes by their possession of swim bladder. Swim bladder generally functions as a float or, in a few fishes, modified to become lung. The bony fishes are divided into two major subgroups: 

subclass Sarcopterygii (lobe-finned fishes)



Subclass Actinopterygii (ray-finned fishes)

Activity:

Q1. What are the major differences between sarcopterygian and actinopterygian actinopterygian bony fishes? Q2. What are the major subcategories of sarcopterygian and actinopterygian bony fishes?

Sarcopterygian Bony Fishes

Sarcopterygian bony fishes are characterized by their possession of fleshy fins with a central supporting bone and distantly located paired fins. These bony fishes are subdivided into two groups: Dipnoi (lungfishes) and Crossopterygii (e.g. coelacanth) as in Table 1.3.


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Table 1.3. Sarcopterygian bony fishes

Category

Habitat

Example

type

Occurre

Remark

nce

Dipnoi

Mainly

Lepidosiren

America

They can

(Lungfishes)

freshwater

Protopterus

Africa

breathe

Neoceratodus

Europe

atmospheric air using lung

Comoro

L. chalmulae is

Archipel

called “living

Crossopterygii

Mainly

(Coelacanth)

marine deep

ago

fossil” i.e. it is

seas

islands

the only living

( Africa)

representativ

Latimeria chalmulae

e of its group

Dear student, please refer to the figures in chapter 6 of your Aquatic sciences and Wetlands Management course module for observation of fin structure and location. In evolution it is assumed that crossopterygians are the earliest bony fishes that probably gave rise to the actinopterygian on one side and to the tetrapods on the other hand.

Actinopterygin Bony Fishes

Actinopterygians Actinopterygians are bony fishes having supporting structures known as rays in their fins. In this group of bony fishes the paired fins are closely located in contrast to those of the sarcopterygian bony fishes. These bony fishes are the most highly successful and diverse of all the fishes and include over 95% of all living fish species predominating in both the fresh and marine waters. Thus, they represent an advanced adaptation of the bony fishes to strictly aquatic conditions. Actinopterygian bony fishes are in turn subdivided into three subgroups namely chondrostei, holostei and teleostei. Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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Chondrostei, Holostei and Teleostei

Chondrostei and holostei have are bony fishes that have soft cartilaginous rays in their fins whereas teleostes have strong spiny rays in their fins. Examples include (chondrostei: sturgeons, bichirs, paddlefishes, spoon fishes) and (Holostei: bowfin, garpikes, gars, etc). Teleostei are the most advanced and the most numerous groups of living fishes that are classified in to a large number of orders, families, genera, etc. Teleosts are fish groups that are important as food and thus important in fishery. Dear student, please refer to chapter 6 of your Aquatic Sciences and Wetland Management course module for more information on all of these fish groups.

1.2. Diversity by Size, Habitat Type and Age Fishes come in various body sizes ranging from about 7.9 millimeters (e.g. Paedocypris progenetica commonly called minnow fish) to about 20 meters long (e.g. whale shark). Fishes occur both in freshwater and marine environments, within which they occupy various types of habitats. For instance, if we consider fishes inhabiting marine environments such as seas and oceans, we find that some are littoral (i.e. live closer to shore), some are pelagic (i.e. live in the open water), and some are demersal or benthic (i.e. occupy near bottom of water). Pelagic fishes, in turn, occur at various depths of water column. For instance, epipelagic fishes occupy a depth of 0 to 200 m, mesopelagic fishes occupy 200-1000 m depth and bathypelagic fishes inhabit a depth below 1000 m, which is very cold. Refer to section 3.1.2 of your Aquatic Sciences and Wetland Management (Biol 302) course module for the various habitats within the marine environments. Fishes also vary in terms of their age ranging from the shortest lived fishes (e.g. goby fishes-whose age is of a few days) to the longest lived fishes (e.g. orange roughly-whose ages can reach hundreds of years). The oldest fish in captivity, the Australian lungfish, is also estimated to be more than 75 years old.


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1.3. Diversity by Sexuality and Brooding Behaviour With respect to pattern of sexuality some fishes are gonochores (i.e. heterosexuals), some are hermaphrodites (i.e. bisexuals) and a few are unisexual. Dear student, please refer to section 2.1.1 of this module for the

details of sexuality in fishes and for the description of each of the pattern of sexuality.

Activity:

Q1. What is brooding in fishes? Q2.Can you mention of the various types of brooding behaviours observed in fishes?

Brooding refers to the behaviours of fishes in which they protect and care their eggs and/or young employing various mechanisms. Most of the fishes such as Nile tilapia ( Oreochromis niloticus ) are mouth brooders protecting their eggs and young by keeping them in the mouth of the parents for extended period of time. Other fishes (e.g. seahorses) are pouch brooders nourishing their offspring in a pouch or sac like the mammalian Kangaroo do. The parent (i.e. the male or the female) that broods or takes care of the eggs and young fish varies among various species. In some fishes males are responsible for brooding (this is called paternal brooding-e.g. Sarotherodon melanotheron), in others females are responsible (this is called maternal brooding -e.g. Oreochromis niloticus ) and in other fishes both parents are

responsible for brooding (this is called biparental brooding-e.g. a catfish species called Phyllonemus typus ).


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1.4. Diversity by Feeding Behaviour Fishes have diverse feeding behavior. Fishes vary with respect to their feeding habits, types of food taken, mechanism of food capture and time of feeding.

Activity:

Dear student, can you give examples of fishes according to their diversities in terms of their feeding behaviours mentioned above?

According to their feeding habits some fishes are parasites (e.g. lampreys), some are scavengers (e.g. hagfish), some are planktivorous feeding on plankton (e.g. whale shark and some bony fishes), some are detritivorous feeding on decayed organic matter known as detritus (e.g. some bony fishes), some are piscivorous feeding on other fishes (e.g. a bony fish called Nile perch), some are molluscivorous feeding on mollusks (e.g. some bony fishes) and some are omnivores feeding on a little bit of everything (e.g. some bony fishes).

According to type of food taken there are two major categories of fishes namely generalists and specialists. Generalist fishes (e.g. omnivorous fishes) feed on everything whereas specialist fishes feed on specific food type (e.g. planktivorous fishes).

According to the mechanism of food capture some fishes are filter feeders that obtain their food by filtering water, some are predators, some are grazers and some are pickers. In relation to the time of feeding some fishes

are diurnal feeding during daytime, some are nocturnal feeding during night or dark time, and some are crepuscular feeding during dawn and dusk.


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Chapter Review Questions

1. What are the characteristics of a typical fish? 2. Give some examples of fishes that are exceptions to: (a) Gill breathing (b) Possession of paired fns 3. What are the characteristics of fishes that make them diverse? List at least five examples 4. What is the basic difference between agnathan and gnathostoman fishes? 5. List down the agnathan fish Classes and distinguish between the extinct and extant groups 6. List down the gnathostoman fish classes and distinguish between the extinct and extant groups 7. What kind of aquatic environments does each of the following fish groups inhabit? (a) Cyclostomes (b) Chondrichthyes (c) Osteichthyes 8. What

are

the

differences

between

the

sarcopterygian

and

actinopterygian actinopterygian bony fishes? 9. List down the three sub-groups of actinopterygian bony fishes and their differences 10. What are the various types of aquatic habitats occupied by various groups of fishes?


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Fish Reproduction and Development Chapter Outline 2.1. Fish Reproduction 2.1.1. Patterns of Sexuality in Fishes 2.1.2. Sites of Embryo Development in Fishes 2.1.3. Fertilization and Spawning in Fishes 2.1.4. Reproduction in Cartilaginous Vs Bony Fishes 2.2. Growth, Development and Recruitment in Fishes

Chapter Objectives Upon completing this chapter, you will be able to: 

Distinguish between the various types of sexuality in fishes (heterosexuality, (heterosexuality, hermaphrodite hermaphrodite and unisexuality)



Distinguish among oviparous, viviparous and ovoviviparous fishes



Distinguish between the fishes undergoing internal and external fertilization



Defines spawning in fishes



Gives examples of fish spawning grounds



Distinguishes between fertilization in cartilaginous and bony fishes



Distinguishes between the various developmental stages of fishes



Defines recruitment in fishes


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2.1. Fish Reproduction 2.1.1. Patterns of Sexuality in Fishes Various ranges of sexuality or sexual pattern are observed in fishes. These include heterosexuality (gonochores), hermaphroditism (bisexuals) and unisexuality. ctivity:

Dear student, what are the differences among these three major forms of sexuality patterns in fishes?

Heterosexuality is the most common form which involves separate male

and female parents. However, there are some considerable variations among the heterosexual fishes. For instance, instance, in some bony fishes sperm cells remain remain viable only for a few seconds once released, and in some live-bearing fishes, the female is able to store sperm for up to 8 or even 10 months, and this sperm is used to fertilize new batches of eggs as they develop. In others, a female may carry sperm from several males at once.

Hermaphroditism takes various forms in fishes. Some fishes serve as both

male and female and thus can produce both egg and sperm. This situation is often known as simultaneous hermaphroditism. In others there is a time sequence of hermaphroditism whereby whereby young fishes reverse their sex as they grow older i.e. males become females and vice versa. This situation is called either sequential hermaphroditism (if sex reversal happens only once) or serial hermaphroditism (if sex reversal takes place more than once). This is

a manifestation of fishes’ sexual plasticity. Nevertheless, the simultaneous hermaphroditic fishes often undergo cross-fertilization with other similar hermaphroditic hermaphroditic fishes. A few undergo external self-fertilization whereby egg and sperm are shed simultaneously into the water from the same individual. Still a few others may undergo internal self-fertilization.


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A few fishes are unisexual i.e. consist only of female population (e.g. Poecilia formosa, of the Amazon River). Such fishes, thus, undergo parthenogenetic reproduction in which unfertilized eggs develop directly into embryos. Yet,

even though development proceeds without fertilization in these females, mating with males of other species is still required just to stimulate egg development. Nevertheless, in all cases of sexuality eggs are produced in ovary (pl. ovaries) and the sperm (milt) in testis (pl. testes). As it is a case with other vertebrates, ovary and testis constitute gonads in fish.

2.1.2. Sites of Embryo Development in Fishes

Activity:

Dear student, Q1. Can you mention the various groups of fishes according to “where” their embryos develop? Q2. Which of these fish groups are predominant? predominant?

Based on “where” their embryos develop fishes can be categorized as oviparous, ovoviviparous and viviparous. Most fishes are egg-layers (i.e. oviparous), thus embryo develops and hatches outside the female’s body in

the environment (water). (water). However, some fishes give birth to live young. Such live-bearing fishes can be ovoviviparous or viviparous.

Activity:

Dear student, we have mentioned above that both ovoviviparous and viviparous fishes give birth to live young. So, what is the difference between between the two groups?


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In ovoviviparous fishes: •

Embryonic development takes place only partly within the female’s body

•

The embryo does not receive any additional nutrition from the mother’s tissue.

•

The mother’s body provides the eggs with respiration (gas exchange) in most cases.

•

Thus, development of embryo depends solely on a food supply from the egg yolk sac.

The process of ovoviviparity in fishes takes any one of the following forms: •

In some ovoviviparous fishes the embryo develops in the egg while the egg is still within its follicular covering within the ovary

•

In other ovoviviparous fishes the eggs are released from the protective follicles into the cavity of the hollow ovary, where development development continues.

In both cases the fishes bear premature young (embryo) whose development relies on yolk for food supply. s upply. In contrast to ovoviviparous fishes, in viviparous fishes embryo stays in the female’s body, until borne, where it is supplied with all nourishment through the mother's tissues.

2.1.3. Fertilization and Spawning in Fishes

Activity:

Dear student, how many modes of fertilization could be found in fishes?


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There are two major forms of fertilization in fishes: internal fertilization and external fertilization. In all live-bearing (i.e. ovoviviparous and viviparous) fishes and in some egg-laying (oviparous) fishes fertilization occurs internally. In contrast, external fertilization is a form of fertilization occurring only in some of the oviparous fishes. Activity:

Dear student, in fishes undergoing internal fertilization the males obviously should have intromittent organs for transferring sperm (often called milt) into the female's body. Q. What are these organs used by such male fishes to transfer sperm into the female’s body? Fishes undergoing internal fertilization use various intromittent organs to transfer sperm or milt from males into the females’ body. For instance, in the male topminnows (an example of a bony fish) the anal fin has been modified into an intromittent organ called the gonopodium , and in sharks the pelvic fins of the male are modified into intromittent organs called myxoptergia or claspers.

In external fertilization females lay eggs in water where the males discharge their sperm (milt) onto the eggs i.e. the process of egg deposition in water (i.e. oviposition) by the female fishes is followed by a release of sperm by the male fishes onto the eggs. Activity:

Dear student, we have discussed above about the modes of fertilization occurring in fishes. Now let’s come to another reproductive process in fish: spawning. What is spawning?


Page 18

Spawning refers to the release of egg and sperm by the female and male

fishes for fertilization. Fishes that hatch from the same spawning event at the same time are termed as cohort in fishery. Fishes often aggregate in pair or group for spawning as in Fig. 2.1a and b respectively.

(a)

(b)

Fig. 2.1. Spawning in fishes (a) Pair Spawning, (b) Group Spawning

Activity:

Q1. How efficient are pair and group spawning in terms of fertilization? Q2. Which of these two major patterns of spawning in fishes is more economical in terms of sperm number released? Q3. Which of these two patterns of spawning ensures more genetic variability?

Group spawning is more efficient, in terms of ensuring fertilization, fertilization, than pair spawning since large number of sperms is released in the former. On the contrary, pair spawning is more economical than group spawning in terms of


Page 19

the number of sperm released. Genetic variability is ensured in group spawning since large number of fishes takes part in the process.

ctivity:

Dear student, studies indicate that fishes usually aggregate before they migrate to a specific site for spawning. Taking river fishes or lake fishes as an example, where do you think that these fishes migrate for spawning?

Areas of water bodies where fishes spawn are known as spawning grounds. Studies indicate that small streams in the watersheds of the rivers or lakes often serve as spawning grounds for river and lake fishes as well as for some marine fishes. For instance, fishes living in any of the large rivers may spawn in small streams or tributaries upstream the river. Therefore, many fish species undertake long distance migrations reaching hundreds of Kilometers to arrive at their spawning grounds. One of the reasons for the fishes to migrate upstream a long distance from their feeding grounds in search for spawning grounds grounds can be a need for well oxygenated sites to lay their eggs.

Activity:

Q1. Based on our above brief discussion about the fish spawning grounds, what do you think could be the effects of dam construction across a given river in relation to fish spawning? Q2. How do you think that such effects of dam construction on fish spawning can be mitigated? Obviously dam construction across a river has an impact of blocking fish migration upstream for spawning. Therefore, during dam construction it is necessary also to construct fish ladders and other bypass systems that would help the fishes migrate past the dams.


Page 20

Activity:

Dear student, in oviparous fishes there is a possibility that some of the spawned eggs could be eaten by the predators or destroyed by other factors. Q. How do such fishes cope with such problems?

In egg laying or oviparous fishes there is a possibility that a huge number of the spawned eggs could be eaten by predators or destroyed otherwise. To cope with the problem, however, each female produces thousands, even millions, of eggs at a spawning. Moreover, fishes undertake various parental care strategies to safeguard their eggs and young.

ctivity:

Dear student, what different parental care strategies do fishes employ to safeguard their eggs and young? Parental care shows great diversity in fishes. •

Hiding: Some fishes, such as the Atlantic herring, form huge schools of

males and females and freely shed their eggs and sperm (milt), and then hide the eggs. •

Nest Building: Other fishes build nests to care for both the eggs and

newly hatched young. The nests may be depressions in the beds of streams and lakes. The eggs and young of nesting fish are commonly guarded by one of the parents, usually the male. •

Mouth Brooding: Some fishes (e.g. Nile tilapia) carry the eggs and

young in their mouth (a condition known as mouth brooding) for long time, fasting until the young are large enough to defend for themselves. •

Pouch Brooding : Others have evolved methods of carrying the eggs

with them, such as in special pouches on the body. Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page 21

2.1.4. Reproduction in Cartilaginous Vs Bony Fishes

Activity:

Dear student, what are the major similarities and differences differences between the reproduction in cartilaginous fishes and bony fishes?

In cartilaginous fishes: •

Fertilization is mainly internal whereby eggs are fertilized inside the females’ body.

•

The males transfer sperm into the females’ genitalia through various intromittent organs organs (e.g. myxoptergia or clasper in shark).

•

The females have cloaca, between their pelvic fins, that contains three openings namely: opening to rectum (at front), opening to vagina (at middle) and opening to urinary duct (at back). Therefore, the males’ intromittent organ penetrates through the middle cloacal opening to discharge sperm into the females’ vagina.

•

In terms of the site of embryo development, most cartilaginous fishes are oviparous and only a few are live-bearers (i.e. viviparous or ovoviviparous).

•

Live-bearing viviparous cartilaginous fishes generally produce small number of offspring that are retained, protected and nourished within the females’ body.

Bony fishes: •

Have well developed reproductive organs

•

Mainly undergo external fertilization (i.e. oviparous)

•

In bony fishes undergoing internal fertilization the males have got an intromittent organ (e.g. gonopodium) to transfer sperm into the female’s cloaca.


Page 22

2.2. Fish Growth, Development and Recruitment Growth refers to an increase in body size (i.e. body length or weight) whereas development refers to the various stages through which the fish passes from the embryonic stage to death.

Activity:

How does fish growth compare with that of other vertebrates?

Unlike most other vertebrates, fish grow throughout their life time, though they grow more slowly as they age. The rate of growth varies greatly, being most rapid where food is most abundant. Growth is commonly quicker in warm regions than in cold.

Activity:

What are the various fish developmental stages? How do they differ from each other?

The terminologies used to describe the life history or developmental stages of fishes could vary for various disciplines such as taxonomy, physiology, fisheries management, etc. Generally we may recognize five stages such as embryonic stage, larval stage, juvenile stage, adult stage and senescent . •

Embryonic stage starts with fertilization and continues until its hatching

(in oviparous fishes) or birth (viviparous fishes). •

Larval stage extends from the time of hatching until the differentiation differentiation of

fins. The larval period in oviparous fish is relatively short (usually only several weeks). Larval fish is very different in appearance from the juvenile and adult stages. However, larvae rapidly grow and change appearance and structure, through a process called metamorphosis, to become juvenile. Initially larval fish depends on

egg yolk for


Page 23

nourishment and gradually switches from its yolk sac to feeding on plankton. •

Juvenile stage begins with the differentiation of fins and continues until

maturity. Therefore, juvenile fish has a more fish-like fish-like appearance. appearance. •

Adult stage starts with the sexual maturity and ends up with the

production of the first gametes. This stage includes reproductive behaviours such as spawning. •

Senescent stage covers a period of a very slow growth during which rate

of reproduction can also be reduced. During this stage a body of fish may undergo rapid degenerative changes.

Activity:

Dear student, in our above discussions we have seen about the fish growth and development. Before we come to wrap up on this chapter, can you mention what recruitment is in fishes? Explain.

Recruitment refers to the number of new juvenile fish or cohorts reaching a

size or an age where they represent a viable target for fishery i.e. recruitment can be defined as the number of new juvenile fishes or cohorts added to the existing fish biomass at a given age or size. Studies indicate that variability in recruitment is a primary factor that drives changes in fish populations. In turn, variability in fish recruitment is caused by densityindependent and density-dependent processes on all pre-recruit stages.

Activity:

Dear student, what are the density-independent and density-dependent processes that affect recruitment?


Page 24

The density independent factors that affect fish recruitment include temperature and food conditions experienced by pre-recruits. The densitydependent processes that affect fish recruitment include competition for food or refuge with conspecifics or offspring of other species. In general mortality rates during the pre-recruit stage are very high. This means a population of faster growing individuals will experience a lower cumulative mortality than a slower growing one.


Page 25

Chapter Review Questions 1. Define heterosexuality, bisexuality and unisexuality in fishes 2. What are the differences among the simultaneous hermaphroditism, sequential hermaphroditism and serial hermaphroditism in fishes? 3. What are the differences among the oviparous, viviparous and ovoviviparous fishes? 4. What are the two forms of fertilization in fishes? 5. How is sperm transferred from male to female in fishes undergoing internal fertilization? 6. What is spawning in fishes? 7. What is recruitment in fishes? 8. List down the various developmental stages in fishes


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Capture Fisheries Chapter Outline 3.1. Introduction 3.2. Fishing Gears and Crafts 3.3. Fishing Methods 3.4. Commercially Important Fishes

Chapter Objectives Up on completion of this chapter, you will be able to: 

Define capture fisheries



Define and distinguish between the fishing gears and methods



List down some major fishing gears often used in capture fisheries



Give examples of major fishing crafts



Give examples examples of commercially important important fishes in the world



Give examples of commercially important species in Ethiopia


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3.1. Introduction Dear student, in this chapter and chapter 4 you will be able to distinguish between two major and broad categories of fisheries. Before, proceeding to the details and discussions of these two subjects it may be wise to take a moment to define what is meant by fisheries. Fisheries (sing. fishery) can be defined as human’s utilization of fish and other aquatic organisms of certain values. This comes in two major forms: capture fisheries (chapter 3) and aquaculture (chapter 4).

Activity: •

Dear student, before you go on reading the following sections take a moment and try to jot down the similarities and differences you think would exist between capture fisheries and aquaculture. You need to refer to chapter 6 of your Aquatic Sciences and Wetlands Management (Biol 302) course module to refresh your memory on the subject.

Capture fisheries (also known as natural fisheries or wild fisheries) can be defined as catching of fish and/or other valuable aquatic organisms for food, recreational, economic or commercial purposes from the natural water bodies such as streams, rivers, lakes, seas and oceans. In contrast, aquaculture is the growing or farming of fish (or other beneficial aquatic organisms) in the natural or artificial water bodies mainly for food or commercial purpose. For more details on aquaculture refer to chapter 4 of this module.


Page 28

Capture fisheries come in various levels or scales. For instance, commercial fishing versus artisan fishing. Commercial fishing is the activity of catching fish and other aquatic organisms for commercial profit, mostly from capture fisheries. Large scale commercial fishing utilizing advanced fishing techniques and materials with high investment is known as industrial fishing. In contrast, artisanal fishing is a term sometimes used to describe small scale commercial or subsistence fishing practices. It uses traditional techniques and traditional fishing boats. It is subject to difficulties in the export process due to inadequate inadequate investment in refrigeration and processing facilities. However, the most important goal of artisan fishing is domestic consumption. Subsistence fishing is fishing for personal consumption.

Activity:

Dear student, Q1. Which scale of fishing do you think applies to Ethiopian fisheries? Explain. Q2. In general, what are the various socio-economic benefits of a fisheries activity to the society?

Ethiopian fisheries are generally small scale and subsistence involving mainly traditional fishing techniques and occasional local fishermen who have alternative means of employment employment such as small-scale agriculture.

As

described in sections 3.2 and 3.3 in most of the Ethiopian lakes and rivers traditional fishing gears and fishing crafts are employed. Nevertheless, as discussed in chapter 5 of this module, fisheries stand a potential economic sector providing various socio-economic benefits to the society. Primarily it is an important source of protein and other nutrients to the poor. It also provides income, employment and even contributes to GDP (Gross Domestic Product) particularly in developed countries with well developed industrial fishing.


Page 29

Activity: •

Dear student, can you mention some of the aquatic organisms including finfish of certain socio-economic values to human being along with their benefits?

Dear student, it is also important to note that in developed countries people also catch fish as a leisure activity. Such kind of fishing is often known as recreational or sport fishing or angling. The people catching fishes in

recreational fishing are thus called anglers. In recreational or sport fishing anglers enjoy themselves by struggling to catch large fishes that are often difficult to fish. In sport fishing, the anglers do not basically take the fish home for consumption. They return them back into the water. This is not practiced in Ethiopia. Aquatic organisms that provide some socio-economic values to human being include vertebrates such as finfish, sea turtles (aquatic reptiles), whales (aquatic mammals), seals (aquatic mammals), dolphins (aquatic mammals); invertebrates such as cnidarians (coelenterates), squids (mollusks), octopus (mollusks), oysters (mollusks), clams (mollusks), lobsters (crustaceans), crabs (crustaceans), shrimps (crustaceans); and algae (aquatic plants). Their values are summarized in Table 3.1.


Page 30

Table 3.1. A summary of of some of the aquatic organisms organisms of certain certain socioeconomic values to human being.

Category

Benefits or values to human

Finfish

Food/Economic values

Sea turtles and Crocodiles

Economic values

Aquatic mammals (e.g. whales)

Economic values

Cnidarians Cnidarians (e.g. corals)

Jewelry /Economic values

Shellfish (mollusks and crustaceans)

Food/Economic values

Algae (e.g. sea weeds)

Ice-cream making and agar-agar production

Thus, exploiting these aquatic organisms that are naturally grown in their natural environment can be termed as capture fisheries whereas growing them under human controlled settings to generate more benefits from the organisms is termed an aquaculture.

Activity:

Dear student, •

From your Aquatic Sciences and Wetlands Management course (Biol 302), chapter 6, you have to recall that there are diverse groups of finfish

including

cyclostomes

(agnathan

fish),

chondrichthyes

(gnathostomatan fish) and osteichthyes (gnathostomatan fish). Q1. Roughly, what percent of the fish species do you think are important in food or commercial fishery? Q2. Which of these fish groups are more important in food or commercial fishery?

Although more than 31, 000 different species of finfish are known to exist only a few species are important in capture fishery. Cyclostomes such as lampreys are almost unknown in fisheries. Whereas the cartilaginous fish Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page 31

such as shark and rays are caught for their commercially important fins and skins respectively. Bony fish, particularly the teleosts (actinopterygians) are more important in both the food and commercial capture fishery worldwide.

3.2. Fishing Gears and Crafts Activity:

Dear Student, we have discussed above about the aquatic organisms that are socio-economically important to human being in fisheries. What various materials and techniques do you think can be used to harvest the organisms in capture fisheries?

Fish and/or other valuable aquatic organisms can be captured using various fishing gears and methods. We shall come to the discussion of fishing methods in the subsequent section (section 3.3). Fishing gears refer to the tools used to capture aquatic resources.

ctivity:

Dear student, Q. If you might have had a chance to encounter some of the fishing gears or have read about them from literature, would you please try to list down some of them before you go on reading the following sections?

The Food and Agriculture Organization (FAO) of the United Nations (UN) identifies the following major types of fishing gears: surrounding nets, seine nets, trawl nets, dredges, lift nets, cast nets, gillnets and entangling nets, traps (such as pots, stow or bag nets, fixed traps), hooks and lines (such as handlines, pole and lines, set or drifting longlines, and trolling lines), and grappling and wounding gears (such as harpoons, spears, arrows, etc). Some Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page 32

of these and the major fishing gears and how they are used are given figures (Fig. 3.2, 3.3, 3.4, 3.5, 3.6). The classification of fishing gears, such as those listed above according to FAO, is based on the combination of the principles of how the fishes are captured and the way the gears are constructed.

Activity:

Q. Which of the above mentioned fishing gears do you think are used in Ethiopian water bodies (lakes and rivers)? Which one is predominant?

The various fishing gears used in Ethiopia include gillnets, beach seines, longlines, hook and lines, scoop nets, cast nets, spears, etc. However, gillnet is mainly used in most of the fisheries accounting for most of the commercial fish production. It is, however, important to note that in some of the water bodies such as in Gambella various types of the traditional gears account for most of the fish capture.

It is important to note that the type of gear used and the way it is constructed and used in catching the organisms may have some damaging effects both on the aquatic organisms organisms and the environment. environment. In the past the technological development of fishing gears was aimed at just increasing fish capture production.

Activity:

Dear student, what do you think may be the side effects of such past time gear development that just targeted increasing the quantity of fish or organisms caught?


Page 33

The consequences of such gear development include: •

Overfishing of certain fish, and under exploitation of others

•

Damaging effect of some gears to the environment including the untargeted catch (both fish and non-fish) and destruction of habitats (e.g. when using dredge nets).

As a result, at present gear development is very much diverted from its past emphasis of increasing capture production, and focused on selective fishing gears with less impact on the organisms and the environment. Moreover, the types of gear to be used and the mesh sizes of the netted gears are determined determined through legislative laws.

Activity:

Q1. Do you think that there exists any legislative law in Ethiopia that addresses the type of gear and the mesh size to be used in capture fisheries? Discuss with any students taking the same course. Q2. In the following sections we will come to the discussions of fishing methods and gears. Before that, please try to discuss with any of your friends taking the same course what factors determine our choice of the fishing gears and methods.

Which fishing gears and methods to be used are based on factors such as where to fish (e.g. small or big water body, shallow or deep water), species and size of fish to be caught, weather condition during the fishing time or day (e.g. sunny or rainy), cost of the gear, boat and fuel, and the market requirements.


Page 34

Activity:

Dear student, Before we proceed to the discussions of the major types of fishing methods, lets us briefly raise some points about the fishing crafts. What do you think are the fishing crafts? Can you give examples?

Fishing crafts are vessels of relatively small (e.g. rafts or boats) or large size (e.g. ships) that are required to navigate on the water bodies while operating the gears for fishing. Modern boats and ships are motorized. However, rafts and traditional boats (e.g. reed boats, coracles and canoes) are not provided with engines. Therefore, Therefore, they are driven driven using paddles paddles (see Fig. 3.1c). 3.1c). Such traditional boats are often common with small scale and subsistence fisheries.

Rafts are structures with a flat top that float and often used to fish in shallow waters (Fig.3.1a). Reed boats are constructed from reeds (Fig.3.1b). Coracles are light boats shaped like a bowl, typically with a frame of woven grass or reeds covered with animal hides or tree barks (Fig.3.1c). Canoes are small narrow boats, usually pointed at bow and normally open on top. It is often constructed from timbers or dugout from a tree trunk (Fig.3.1d). A fishing ship is also shown in Fig.3.1e.


Page 35

(a)

(c)

(b)

Paddles e

(d)

Fig 3.1. The various types of fishing crafts. (a)Modern raft, (b) Reed boats, (c) Coracle boats, (d) Canoe boats, (e) Fishing Ship

Fishing crafts (boats or ships) can be used to set the gears in the water (e.g. gillnets) so that the fishes are caught after the gear setting (Fig.3.2a). Alternatively, fishing crafts can be used to actively tow or pull the gears in the water to immediately catch fish (Fig.3.2b).

Fishing craft Gillnet

Dredge nets

(a)

(b)

Fig.3.2 (a) A gillnet set in water at given point, (b) A fishing craft or vessel towing dredge net in the water. Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page 36

ctivity:

Dear student, Q1. Among the various types of fishing gears we mentioned above according to FAO, which ones are to be set at a given point in the water body to catch fish after being set, and which ones are to be towed or pulled in the water column by the boats or ships to catch the fishes immediately? immediately? Q2. In this respect can you categorize the various fishing gears into some broad categories? Q3. Which types of fishing crafts do you think are used in Ethiopian fisheries? What can you say about the level of development of Ethiopian fisheries in this respect?

The various types of fishing gears can be broadly categorized as static (passive) and active gears. Static gears are set at a given position in the water and left for some times until the fishes come to the gear to be caught. These include gillnets and entangling nets, trap nets, long-lines, etc. On the other hand, active gears are towed or pulled in water column using fishing crafts to catch the fish. Therefore, in case of the static gears the probability of fish being caught by the gears depends on the probability of the fish moving into the gear; whereas in active gears it is the gear that should move to the position where the fishes are. These include trawl nets, seine nets, dredge nets, lift nets, scoop nets, cast nets, trolling lines, jigging lines, hand lines, Spears, etc. In developed countries, modern technology has yielded electronic navigation and sophisticated fish-finding equipment that can locate the fish . For example, Colour echosounder helps to locate the depth at which the fish are Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page 37

located. Colour net recorder, used along with the echosounder, is used to give

information about the gear gear being being used used and and the fish moving moving into it i.e.

the quantity and types types of fish fish moving in to the gear. gear.

3.3. Fishing Methods Fishing methods refer to the various ways the fishing gears are employed in capturing the organisms. It, thus, means that the same fishing gear can be used in many different ways. The methods used to catch the finfish and shellfish are basically similar. However, some differences exist. The major types of fishing methods used for finfish include netting, lining, trolling, trawling and seining. Trawling, dredging, jigging and pots are often used for capturing shellfish (such as squids and crabs).

Activity:

Dear student, try to think of the differences and similarities that exist among the major fishing methods such as netting, trawling, seining, lining, trolling and dredging before you pass on to read the following sections.

In netting method of catching fish fishing gears such as gillnets and entangling nets are employed. These nets are typically long, narrow and flat with diamond shaped meshes. The nets are set stretched, keeping their meshes open, in the water column with “weights” at the bottom edge and supporting “floats” at the top edge (Fig.3.3). Fishes are thus caught when attempting to pass through the meshes which catch usually in their gills. Hence, gillnets are named so because fishes are caught when their gills are snared in the net’s mesh. Gillnets are static gears that are set at a given point and the capture of fishes depends on the fishes moving into the gear sometimes after setting of the net. One should wait at least overnight to get Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page 38

could fish catch after setting the gillnets. For this reason they are said to be the set-and-wait set-and-wait gears. Gillnets are easy easy to construct and often often supplied by the net makers. They are cheap and also relatively easy to operate, and consequently have been extensively used in reservoirs and lakes fisheries throughout the world. Limitations of gillnets, however, include their requisite of a boat from which they are set and lifted and this imposes an additional cost. Moreover, gillnets are vulnerable to theft and thus fishermen need to frequently spend the night watching over their gear or devise ways to conceal the floats.

Floats

Mesh

Weights

Fig. 3.3. A gillnet with with mesh, floats and weights

Activity:

Dear student, Q1. What do you think are the purposes of putting “weights” and “floats” on the edges of gillnets while setting them in water ? Q2. What local materials do you think can be used as “weights” and “floats”?


Page 39

The “floats” and the “weights” help the gear (gillnet) remain float in the water column during setting. The gillnet mesh sizes matter in catching fish of appropriate or desirable size. Too small mesh sizes are often not recommended as they often target the smaller or young or larval fishes that have not fully grown. In contrast, too large mesh sizes catch only large size fishes. Thus, it is recommended recommended to use an appropriate mesh size that does not catch untargeted fishes or other organisms.

Trawling method of catching fish involves towing or dragging of the

especially designed trawl nets using one or two fishing vessels such as boats (Fig.3.4a). Trawling is the most important commercial fishing method used to catch a range of species especially the deep habiting habiting ones. However, its use is limited because of its high by-catch (i.e. untargeted catch). Dredging is towing a rigid steel-framed dredge net along the bottom of the water body with a fishing vessel to catch shellfish such as scallops and oysters (Fig.3.4b). Therefore, unlike gillnetting, trawling and dredging are active fishing methods. However, all the methods employ nets constructed in different ways.

Fishing vessels

Dredge nets

Trawl net

(a)

(b)

Fig. 3.4. (a)Trawling method, (b) Dredging method


Page 40

Activity:

Dear student, what do you think is a by-catch in the process of fish capture? Can you give examples?

By-catch refers to unwanted or untargeted organisms captured by the fishing gears. It can be fishes of unwanted size (e.g. too small size or young fishes) or other animals than fish unwanted in the process of fishing. By-catch is considered a loss in fishery and it is environmentally deleterious. deleterious.

Long-Lining involves the use of fishing gears known as long-lines. In this

method the long-lines consist of a main line with hooked and baited short lateral lines (known as snoods) attached at intervals. The line is anchored at each end and held at the surface by floats (Fig.3.5). This is a static or passive gear method.

Floats Main line

s d o o n S

Weights

Fig. 3.5. A long-line with its baited and hooked lateral snoods

Activity:

Dear student, what do you think is a bait and its purpose in catching fish?


Page 41

Bait is anything used as food by the target fish or lure attached to the ends of the snoods or the lines to attract fish to the lines. The lured fishes are then caught by the hooks at the t he tips of the snoods when attempting to eat the bait.

Trolling method only slightly differs from long-lining method in that many

parallel baited and hooked lines are towed behind a boat. The difference is that there is no main line in this case and all the lines are of same size (Fig.3.6a). Jigging is a method that involves continuously lowering and retrieving lines provided with lures from the fishing vessel (Fig.3.6b). It is mainly used to catch squid in marine fishery. Thus, unlike long-lining, trolling and jigging are active methods of fishing. However, all utilize lines as fishing gears in different ways.

(a)

(b)

Fig. 3.6. (a)Trolling method, (b) Jigging method

Activity:

Dear student, now we are coming to the conclusion of our discussion on the fishing methods. Have you ever heard of a fishing method that involves the use of fish poisons or toxins? Can you give an example in Ethiopia?

Poison fishing involves the use of poisons or toxins extracted from some plants. The poisons are added into the whole water body in order to Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page 42

intoxicate the fishes. The fishes are then easily collected when they become unconscious because of the intoxication. Plants used to extract such fish poisons in Ethiopia are mainly Milletia sp (Locally: Birbira); and generally in Africa involve Euphorbia sp. (Locally called Quliqual in Ethiopia). However, the use of such poisons is generally illegal due to the effects of the poisons on the other aquatic organisms. The poisons might also be toxic to human if consumed via fish.

3.4. Commercially Important Fishes

According to the Food and Agriculture Organization of the United Nations (FAO, 2002, 2002, 2004, 2006, 2008, and 2010), a publication

of the United

Nations, the commercially important marine finfish species worldwide include Anchoveta, Alaska Pollock, Atlantic herring, Skipjack tuna, Japanese anchovy, Chilean jack mackerel, mackerel, Largehead Largehead hairtail, Chub mackerel, mackerel, Capelin, Blue whiting, Yellowfin tuna, Salmon, Groundfish and Tuna.

The

commercially important freshwater finfish species important worldwide include carps, barbells, (and other cyprinids), tilapias and other cichlids, shads, salmon, trouts, smelts, catfish, salmon, s almon, and Nile perch. Commercially important fish species in Ethiopia are summarized in Table 3. 2. Dear student, please refer to your Aquatic Sciences and Wetlands Management (Biol 302) course module, section 6. 2. 1, for details on some of the economically important families of fishes in Ethiopia.


Page 43

Table 3.2. Commercially important fish species in Ethiopia (Source: Ethiopian Institute of Agricultural Research, EIAR)

S. No. Scientific name

Common name Vernacular name

1

Lates niloticus

Nile perch

Nech asa

2

Oreochromis niloticus

Nile tilapia

Qoroso/Chogofe

3

Barbus species

Barbus

Bilicha

4

Labeo species

Labeo

Barbo/Lebi

5

Clarias garipienus

Cat fish

Ambza

6

Bagrus dockmac

Bagrus

Kerkero

7

Polypterus bichir

Nile bichir

Eguwella

8

Gymnarchus niloticus

Gymnarchus

Wit

9

Malapterurus species

Malapterurus

10

Crussian carp

Carp

Daba

11

Distichodus niloticus

Distichodus

Piro

12

Hydrocynus forskali

Hydrocynus

Weri

13

Heteroticus niloticus

Heteroticus

Ediwela

14

Citharinus citharinus

Citharinus

Ajaka

15

Synodontis species

Synodontis

Akok


Page 44


1. What is fishery? 2. What are the two major forms of fisheries? 3. Define capture fisheries 4. List down some examples of fishing methods and give their differences 5. What is a fishing gear? 6. List down some examples of fishing gears and how they are used 7. What is a fishing craft? 8. List down some examples of fishing crafts and their differences 9. Give examples of commercially important fishes in the: (a) World (b) Ethiopia


Page 45

Aquaculture Chapter Outline 4.1. Introduction 4.2. Types of Aquaculture 4.3. Aquaculture Systems 4.4. Establishment of aquaculture 4.5. Sustainability of aquaculture


Define aquaculture and distinguish between aquaculture and pisciculture



Discuss the importance of aquaculture practices



Distinguish between the various types of aquaculture (pond, cage, pen etc)



Distinguish among the various types of aquaculture systems (extensive, intensive, semi-intensive, etc)



Discuss the factors to be considered (e.g. site and species selection) when planning to establish an aquaculture



Discuss the factors that should be considered in sustainability of aquaculture


Page 46

4.1. Introduction Aquaculture can be defined as rearing or farming of aquatic animals and plants in a natural or artificial water bodies under human controlled setting. The usage of the term aquaculture is often universal referring to the farming of all valuable aquatic organisms such as finfish (e.g. tilapia, perch), shellfish (e.g. mollusks and crustaceans), coelenterates (e.g. corals), aquatic mammals (e.g. whales and sea lions), aquatic reptiles (e.g. turtles and crocodiles), and algae (e.g. phytoplankton and seaweeds)as described in section 3.1 of this module. Therefore, strictly speaking a form of aquaculture that involves rearing of only finfish is termed as pisciculture (pisc meaning fish; culture meaning farming or rearing) . However, it has become commonplace to use the term aquaculture restrictively just to mean fish farming.

Activity:

Dear student, what do you think are the various benefits of aquaculture?

Aquaculture practices are important primarily for providing foods and nutrition to the human being particularly in developing countries where there is critical shortage of food. Moreover, aquaculture practice is important in fishery management and biodiversity conservation. As discussed in chapter 5 of this module, most of the world capture fisheries have already peaked off and even started declining. In this respect, aquaculture can serve as an alternative source of fish and shellfish in the face of a decline in capture fisheries. In addition, it helps to rear and keep artificially fish species that have been heavily exploited and whose status has been endangered through natural fishery.


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Activity:

Dear student, as described above other aquatic organisms, than finfish, can be reared in aquaculture. Q. Is there any such farming in Ethiopia? What do you think is the socioeconomic benefit of such farming?

Other aquatic organisms than finfish can also be reared in aquaculture. For instance, there is a Nile crocodile farm in Ethiopia, commonly known as crocodile ranch , in Arba Mich on the edge of Lake Abaya, mainly for its skin

which is processed into leather products such as shoes and ladies handbags. Moreover, the farm has been a source of tourist attraction. The farm, however, suffers heavy flooding especially during the rainy seasons causing the death of thousands of crocodiles. The farm can generate considerable amount of foreign currency for the country, through export of the crocodiles skin and tourist attraction, if properly managed. Other aquatic organisms such as shellfish and algae are also reared for various socio-economic reasons including food and commercial benefits.

Activity:

Dear student, in our discussions above we have defined and described what an aquaculture is. Assume that you have dug a pond and filled with water for the purpose of fish farming. Where do you think that you can get fish “seeds” to start rearing fish in your pond?

The process of introducing fish seeds (often larvae) into a water body is termed as stocking. The fish seeds required for stocking a water body can be obtained from fish hatchery stations or alternatively they can be collected from other natural water bodies. However, the latter case may have an impact on the fish population in the natural water bodies and thus it is Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page 48

preferable to get fish seeds from the hatchery stations. In Ethiopia, the Sebeta Fish Culture Station (currently organized as the National Fish and Other Aquatic Life Research Center), located near Addis Ababa, used to serve this purpose since its establishment in 1975.

4.2. Types of Aquaculture Aquaculture establishment comes in various forms including pond aquaculture, cage aquaculture, pen aquaculture, tank aquaculture, etc. Pond aquaculture has been practiced since 4000 years ago in Asia and later adopted to Europe. It has shown only little changes over centuries being limited to fresh water pond system owned by a single household producing fish for subsistence i.e. just to cover the daily food need. Aquaculture ponds can be

either with soil bottom (known as earthen ponds) or concrete-lined ponds.

Activity:

Dear student, what is the difference between soil bottom ponds and concrete-lined ponds?

The former are often used for extensive aquaculture system whereas the latter are used for intensive and semi-intensive aquaculture systems. The choice of species for stocking and rearing in all types of aquaculture systems including ponds, pens and cages is more or less governed by principles, including fast growth in confinement, good consumer acceptance, high tolerance to a wide range of environmental conditions, resistance to disease, ready supply of fish seed for stocking and ease of culture and management. Accordingly, fish species commonly raised in freshwater ponds include tilapia, catfish, carps, eel and salmonids. Similarly different species of fish are reared in brackish and marine water ponds. Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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Activity:

Dear student, what should one do in order to have successful pond aquaculture?

Successful pond aquaculture requires us to regularly accomplish pond water management and pond maintenance activities. Water in the pond should be kept at certain levels and its quality should also be frequently monitored for optimal fish growth. This is particularly important in intensive and semiintensive culture systems where large amounts of fish wastes are continuously excreted into the pond and where excess, unconsumed fish feeds add to the bottom causing water pollution. In general, in fish pond culture, the pond water should be frequently freshened by the entry of new water from the river or another water source through the supply canal while old water is drained through the outlet or drainage gate, and dumped into the receiving water bodies (e.g. river, seas) through the drainage canal.

Activity:

Dear student, we have seen above that water management is one of the important factors in successful pond aquaculture. What other factor is re uired uired for the succes successful sful ond a uacult uaculture ure??

Besides the water management procedures, pond maintenance procedures should also be executed for healthy pond. These include regular application of fertilizers to facilitate the growth of phytoplankton that serve as food for planktivorous or herbivorous fish, addition of lime to regulate water pH at alkaline or near-alkaline levels, application of pesticides to prevent pests, use of screened gates to prevent entry of predators, monitoring of the fish stock for growth rate determination as a basis of feeds and water management, and regular pond repairs and maintenance. Intensive and semi-intensive culture systems may not require addition of fertilization since they are


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dependent on externally supplied food than the natural food in the ponds. Up on successful culturing procedure marketable-size fishes are harvested at the end of the culture period by draining the pond or reducing the water level and using harvesting nets to catch the fish. Although pond culture has been a tradition in aquaculture practice for so long time, fish culture in natural water bodies such as lakes, rivers, estuaries and marine coastals, using enclosed materials such as cage, pen and tank, has been started as recent as 1920s in Africa and Asia. Therefore, cage and pen aquaculture represent the latest developments in the growth and improvement improvement of aquaculture practices. At present they account only for small portion of the aquaculture despite their rapid growth.

Activity:

Dear student, how do cage and pen aquaculture differ from pond aquaculture? What is the difference between cage and pen? Cage and pen are enclosures or confinements constructed from the supporting frames (of various materials such as bamboo, wood, or metal) and covered with nets. Although there are people who use the terms cage and pen interchangeably, these are two different enclosures according to FAO (1984). A fish cage is totally enclosed on all, or all but the top, sides by mesh or netting (Fig. 4.1.), whereas in pen culture the bottom of the enclosure is formed by the lake or sea bottom (Fig. 4.2). Therefore, fish pens are fixed but fish cages can be either fixed or floating. Moreover, fish pens theoretically have no limit to their size or area while cages cannot exceed 1000 m

2

in area for

reasons of the quantity of net required for cage construction and manageability of operation.


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(b) (a) Fig. 4.1. (a) A typical floating fish cage with fish inside, (b) Many floating fish cages set in the water

Extra or more nets are required in cage construction, than in pen, because the floor or the base of the cage should be close unlike in pens. Moreover, the techniques used to harvest fish from the two systems are different. In cage culture the cages should be lifted up and then the fish are scooped whereas in pen culture nets are used to catch the fish from the enclosures or the pens.

(a) (b) Fig. 4.2. (a) A typical fish pen outside of water, (b) A fish pen set in a water body


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Cage and pen aquaculture systems have both advantages and limitations. Cages and pens have several advantages over pond culture systems. These include: 

They are easily applicable in existing types of water bodies such as lakes, rivers, reservoirs and marine coastal waters.



They provide higher productivity than the ponds with minimal inputs and at lower costs to develop and operate.



The phytoplankton from the main water body, in which the cage or pen is set, serve as food for the fishes being reared in the cage or pen



Therefore, they help to clean up eutrophic waters through the culture of planktivorous or herbivorous species that feed on phytoplankton.

Limitations of cage and pen aquaculture include various e nvironmental impacts.

Wastes produced by the fishes in the cages or pens enter the water body and cause various environmental problems such as eutrophication, depletion of oxygen and other consequences. Moreover, there is a possibility of fish disease transfer in both directions i.e. between the wild fish species living in the natural water body and the reared fishes contained in the cages or pens. Predators from the natural water body may also attack the culture fishes within the enclosures. Tank aquaculture involves the use of tanks (more or less similar to the water tank used to temporarily store water) constructed from different materials in various designs as shown in Fig.4.3. Fish tanks are constructed in various designs such as rectangular or circular, and often used in intensive indoor fish rearing activities such as in hatchery. See section 4.3 for the definitions of various aquaculture systems such as intensive, extensive, etc systems.


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Lateral view

Cross sectional view

Fig. 4.3. Circular fish aquaculture tanks

ctivity:

Dear student, as you read various literature you come to know that pond and tank cultures are often referred to as land-based aquaculture systems, whereas cage and pen cultures are called water-based aquaculture systems. Why? Please discuss with any one of the students taki takin n this this cou cours rse. e.

4.3. Aquaculture Systems

Various fish farming or aquaculture systems exist based on stocking density, level of input, methods or techniques of farming, etc. These include extensive farming, intensive farming, semi-intensive farming, integrated farming, circulatory farming, monoculture farming, polyculture farming, monosex farming and ranching.

In extensive farming low density fish are stocked and farmed in large areas of water bodies. The fishes mainly naturally feed and grow only with less


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input of capital and labour. This is, therefore, an old system that can be applied only to the naturally fertile water bodies. It means that if the natural fertility of the water body in which we are rearing the fish is less, the productivity (i.e. the quality and quantity) of fish will be less. Intensive farming is the opposite case of extensive farming. In intensive fish farming,

high densities of fish are reared in a water body and the fish rely almost entirely on the feed externally supplied by the farmer. Therefore, this is a costly system that requires high labour and capital input. It, however, gives high fish production if the input required is properly provided. provided.

Activity:

From our discussion of extensive and intensive fish farming above, what do you understand about the: Q1. Differences between the two forms of farming in terms of stocking density? Q2. Advantages and limitations of each form of farming in terms of cost and amount of production? Circulatory systemto isinvest a system of aquaculture or fish farming Q3. If you happen on fish farming, which of these twowhereby systems the

exhausted is chemically treated to be taking re-used. do you gowater for? Discuss your stand withand anycirculated of your friends thisThis system of farming is often practiced as an extreme case of intensive farming. course.

Semi-intensive farming represents an intermediate form of farming in

which the farmer provides some additional feeds and/or fertilizer to supplement the naturally available food in the water. Fish farming in earth ponds can represent such system of aquaculture.

In Integrated system fish farming is combined with other animal husbandry such as poultry or cattle farming. The purpose of such integration is to use excreta or faeces released from the animals husbandry that will serve as manure to stimulate the growth of phytoplankton. This is because phytoplankton

are

important

food

sources

for

the

planktivorous


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(herbivorous) fishes. However, it is possible to use inorganic fertilizers to increase fertility of the water if the integration is not possible. In fish aquaculture it is possible to rear only a single species or many species of fish in one water body. The former case is known as monoculture system and the latter form is termed as polyculture system.

Activity:

Dear student, what do you think is the difference between the monoculture and polyculture systems of fish farming?

Monoculture system allows very high fish production with the use of additional feeds since it reduces species competition for feed and other resources. It is applicable in water bodies with less or no niche diversity which the different species can occupy. In polyculture system the different fish species should have complementary feeding habit and different niches in order to effectively utilize the resource in the water body. It yields a higher production than monoculture system if the water body in which the fish are reared is fertile and has diversified niche. It is important to note, however, that there are piscivorous (fish eating) fishes (e.g. Nile perch), and such fishes don’t have to be kept in the same water body with the other nonpiscivorous fish species. This is because the piscivorous species eat and destroy the other non-piscivorous fish species. Activity:

Dear student, the monoculture and polyculture systems we discussed above are based on the number of species farmed in a given water body. What about a fish farming system according to fish sex?

It is possible to keep both sexes of fish (male and female) in the same water body in the process of fish farming. However, this may have a side effect of causing unwanted breeding among the fish. In that case it is good to rear Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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male and female fishes in separate water bodies. Such system of fish farming is known as monosex culture system. However, it can be a difficult task to carryout especially in large scale farming.

Ranching is an exceptional form of aquaculture in which fish are reared in

hatcheries, and then released into the natural water bodies to naturally feed and grow, and ultimately recaptured. According to FAO (1997) this form of fish farming can also be called stock enhancement enhancement or culture-based fisheries. fisheries. Therefore, strictly speaking ranching may not be considered an aquaculture. It is mainly practiced in marine water bodies by countries such as Japan. ctivity:

What do you think are the advantage and limitation of such form of aquaculture?

In ranching, fish naturally feed and grow. It, thus, reduces input costs. It, however, may be difficult to re-capture the fish back especially in big water bodies such as in marine environments.

4.4. Establishment of Aquaculture

There are many factors to consider during aquaculture development. The two important factors are species and site selections. Species selection is one of the most important factors to be considered in establishing aquaculture.

Species

are

selected

according

to

their

biological

characteristics, economic and market conditions, and effects on environment. In aquaculture one should go for the selection of species with desirable biological characteristics such as feeding habit, reproduction rate, growth rate, etc.


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Activity:

Q. What kind of biological characteristics of fish can be considered as desirable in aquaculture practices?

A good quality fish for aquaculture should be the one with a feed requirement that can be easily supplied, and have faster reproduction and growth rates so that production can be obtained in a relatively shorter period of time. It is very expensive to supply the high-cost fishmeal that carnivorous fish species require to grow; thus farming of the herbivorous fishes is both more economical and easier to integrate with other conventional farm activities.

Piscivorous (carnivorous) fish Planktivorous fish Zooplankton

Phytoplankton

Fig.4.4. A pyramid of trophic relationship among the aquatic organisms As you move from the base of the pyramid (i.e. from the primary producers) to top of the pyramid, the amount of energy that flows from one level to the other becomes less and less. It means that if you (as a human being) feed on a kg of planktivorous fish you get more energy than from eating the same amount of piscivorous fish (e.g. Nile perch). On the other hand, raising in order to obtain a kg of carnivorous fish from aquaculture production, we Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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need to supply more than a kg of fish meal (as a feed) to the carnivorous fishes, and which is more expensive. However, the raising of herbivorous or planktivorous fishes is less expensive since it is possible to increase the production of phytoplankton by increasing the fertility of the ponds as discussed in sections 4. 2 and 4.3. Moreover, a farmer planning for fish aquaculture should consider that the fish species he/she is rearing are demanded on market and with good price. While considering the biological and market conditions in species selection, one should not undermine the effects the fish might produce to an environment. For instance, common carp ( Cyprnius carpio L.)has been reported to have some some environmental environmental impacts. impacts.

Carp contribute contribute to poor

water quality by uprooting vegetation and stirring up sediments during feeding, leading to increased turbidity. Carp have significant effects on the aquatic plants both through direct grazing and uprooting in search of prey, leading to a reduction in plant density and biomass (Sidorkewicj et al .,., 1998). Turbidity of the water reduces light penetration, which can make it difficult for the other fish that rely on sight to feed. Reduced light can also decrease plant growth, and suspended sediments can smother plants and clog fishes' gills. There have been suggestions that carp may increase the likelihood of eutrophication or algal blooms by preying on animals that eat algae and stirring up nutrients trapped in bottom sediments.

Activity:

Dear student, from our above discussion about species selection for aquaculture establishment, what are the characteristics or conditions of fishes that we need to take in to account? List them and write down how each is important.

Site selection is another important factor of consideration in establishing

fish farming. In selecting site for both for the water-based and land-based Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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farms the limnological characteristics such as water quality and quantity should be studied and determined if they are suitable for the fish species of our choice.

Activity:

Dear student, which characteristics of water bodies should be studied in site selection for aquaculture? aquaculture? The various limnological characteristics that need to be studied in this regard include the amount of dissolved oxygen, water temperature, conductivity, pH, amount of various nutrients such as nitrogen and phosphorus. The measurement and determination of these characteristics are important because various fish species have different requirements for the amount of dissolved oxygen, water temperature, pH, etc. Moreover, both the land-based land-based and water based aquaculture systems should take into account of accessibility and availability of man power for construction and operation. The site should be preferably readily accessible by land or water transport; close to sources of inputs such as fish seeds, feeds, fertilizers, and markets, fish ports, processing plants, and ice plants; and linked by communication facilities to major centres. In addition, for a pond culture, the engineering and design of the pond need to be carefully carried out following standard engineering procedures. For instance, the pond should be constructed in such a way that it will not be over flooded and it is also good to have a pond underground drain out or spillway. The location of the pond should also be in such a way that it can regularly obtain water supply. It is also better to not to have ponds constructed in close proximity with big trees and thick vegetation which entail large expense for clearing. The soil quality of a pond should be, preferably, clay-loam or sandy-clay for water retention and suitability for diking. The soil pH should be alkaline (≥7) to prevent problems that result Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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from acid-sulphate soils such as poor fertilizer response, low natural food production, slow growth of culture species and probable fish kills.

Activity:

Dear student, in our discussion above about site selection in aquaculture establishment we mentioned that factors such as water quality parameters, site accessibility, availability of human power, design or engineering of the pond, location of the pond and pond soil characteristics need to be carefully studied. Please list down each of these factors in your note book and then write down how each is important.

4.5. Sustainability of Aquaculture ctivity:

Dear student, in sections 4.1 through 4.4 we have discussed about aquaculture and mentioned that it can be taken as an alternative source of fish to the exhausting capture fisheries. Do you think that aquaculture will continue to be sustainable source of fish? Explain.

Aquaculture is an important sector in providing fish especially to the poor. Yet, its sustainability is confronted with some limitations. Studies indicate that aquaculture practices compromise water quality, cause environmental and public health problems, involves risks of introduction of exotic or nonnative species and genetic problems to the wild populations through escapes from aquaculture installations, may compete with the land-based agricultural activities for land, and with capture fisheries for water and species. Water quality parameters such as water temperature, amount of dissolved oxygen, pH, conductivity, amount of phosphorus and nitrogen, etc, of Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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aquaculture water in ponds or tanks can be affected as a result of the feeding regime and metabolism of the fish. For instance, fresh water fish add ammonia and salts to the water through their metabolic processes. Management activities including cleaning of the tanks and disease treatment using antibiotics may also affect aquaculture water quality. This in turn may affect the aquaculture setting itself and the receiving water bodies (e.g. rivers) to which the exhaust water is discharged. This in turn causes serious environmental and public health problems. Moreover, in cage and pen fish culture fish wastes collect on the bottom, damaging or eliminating bottomdwelling life. Fish wastes are organic and thus can also decrease dissolved oxygen levels in the water column. Aquaculture can be the cause of the introduction of non-native species from one area to another. Such introduction of exotic or non-native fish species can cause the loss of food, habitat, spawning or reproduction areas, etc of the native or indigenous fish species. This ultimately leads to the decline or loss of the native species, and thus reduces biodiversity. Farming of fishes higher in food web trophic levels, such as carnivorous or piscivorous fishes, requires us to feed them with other fish lower in food web trophic levels (see Fig. 4.4). As discussed in section 4.4 of this module, in relation to species selection for aquaculture, one has to give more fish meal to such carnivorous fishes. This has two side effects: first, we deplete fishes in the natural water because we get the fishes to be given as feed to the carnivorous fishes by catching from the natural water bodies; second, it is expensive to afford such fish meal to the carnivorous species and it is not profitable. Some aquaculture fish such as salmon and tilapia have been genetically modified to improve growth rate and other characteristics. This has caused a fear that farmed fishes escaping from aquaculture setting may reproduce with the wild pollution causing genetic pollution such as production of Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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offspring with undesirable characteristics. Moreover, Moreover, the effect of eating such genetically modified fish on human health has not been confirmed. In addition aquaculture can lead to the degradation of the physical habitat through lowering of the ground water level of the coastal areas when diverting water for the ponds, destruction of the coastal vegetation leading to erosion.

ctivity:

Dear student, in our discussions so far, I hope, that you have come to know that aquaculture is an important source of fish, especially to the needy, in the face of a decline in fish production from the capture fisheries. However, its sustainability is full of challenges. How do you think think that that it it is is ossibl ossible e for for a uacult uaculture ure contin continue ue sustai sustainab nabll ?

So far, research and commercial feed improvements during the recent decades (1990s and beyond) have lessened many of the problems associated with farming of carnivorous fishes. Also in order to reduce aquaculture competition with other land-based agricultural activities for land, it is imperative to integrate both sectors to maximize synergistic and minimize antagonistic interactions, towards the common benefits. Much of the aquaculture problems, however, still remain unsolved. Therefore, the future prospect of aquaculture, as a potential source of fish, is based on further research undertakings in order to reduce or avoid the associated limitations by improving the techniques.


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1. What is aquaculture? 2. What is pisciculture? 3. What are the various importances of aquaculture practices? 4. What are the differences among pond culture, cage culture, pen culture and tank culture? 5. What are the differences among extensive culture, intensive culture and semi-intensive culture? 6. List down and discuss the factors to be considered when planning to establish an aquaculture 7. What are factors that are related to sustainability of aquaculture?


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Status and Prospects of Capture Fisheries and Aquaculture Chapter outline 5.1. World Case 5.2. Ethiopian Case

Chapter Objectives: Up on completing this chapter, you will be able to: 

Discuss the status of capture fisheries production on a global scale



Discuss the status of aquaculture production on a global scale



Explain the trends in the fisheries productions coming from capture fisheries



Explain the trends in the fisheries productions coming from aquaculture



Discuss the trends in the fisheries productions coming from both capture fisheries and aquaculture



Discuss factors that are accounted for the decreasing trends in the fisheries productions coming from the capture fisheries



Tell the capture fisheries production potential of Ethiopia



Tell the actual capture fisheries production of Ethiopia



Discuss the past development development history of Ethiopian fisheries



Discuss the present development status of Ethiopian fisheries



Discuss the important points about the Fisheries Legislation of Ethiopia


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5.1. World Case

Activity:

Dear student, Q1. Have you ever heard about the Millennium Development Goals (MDGs)? Q2. Which of the millennium development development goals may relate to fisheries?

Millennium Development Goals (MDGs) are eight objectives set to be achieved by all the United Nation member states, which Ethiopia is a member, by the year 2015. Eradication of extreme poverty and hunger is one of those eight goals of MDGs. In this regard, capture fisheries and aquaculture can be considered potential sectors that can contribute to the improvement of the livelihood of many people in the poorest countries, and thus help in the achievement of the MDG goal.

Activity:

Dear student, what does the state of fisheries and aquaculture look like? In other words, is the production from the fisheries and aquaculture sectors increasing or decreasing?

Data reported by FAO (2000, 2008, 2010) about the State of World Fisheries and Aquaculture, are attached in Appendix 1.


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Activity:

Dear student, carefully look at the trends in fish production from total capture fisheries and total aquaculture of the world, both

from inland (e.g. lakes and rivers) and marine (e.g. seas and oceans) water bodies, from the year 1996 – 2009 in the three tables given in Appendix 1. Q1. From which type of waters (inland or marine) is most of the fish production generated in: (a) Capture fisheries? (b) Aquaculture? Q2. What trend do you see in the total production coming from the: (a) Capture fisheries? (b) Aquaculture? Q3. What can you say about the future prospect of capture fisheries as a source of fish production on a global scale?

Data from the three tables in Appendix 1indicate that most of the capture fisheries production comes from marine fishing; whereas most of the aquaculture production is obtained from inland waters.

Dear student, if you carefully observe the data given in all the three tables in Appendix 1, you can learn that capture fisheries has shown an increasing trend at a decreasing rate and thus has become plateau from 1990s onward from 6% per annum in 1950s and 1960s, to 2% per annum in 1970s and 1980s, to almost zero growth rate in 1990s. In other words, production from the capture fisheries has already reached its maximum potential and even started declining. Careful observation of the data also shows that capture


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fisheries has peaked off both in the inland (e.g. lakes and rivers) and marine waters (e.g. seas and oceans).

ctivity:

What factors do you think have caused such decline in capture fisheries production on a global scale?

Many of the world’s capture fisheries have been pushed to the brink of their productive capacity by overfishing or overharvesting due to increased human pressure. For instance, studies indicate that approximately about one half of the major marine fish stocks are already fully exploited. Moreover, Pollution, degradation of aquatic habitats, and other forces compound the pressure, with climate change posing a potentially enormous threat. The expected impacts of climate change, such as greater shifts between drought and flooding, higher water temperatures, and heavier storms in coastal areas, can alter fisheries in ways that have major implications for ongoing production of fisheries.

Activity:

Dear student, we have seen above that fish production from capture fisheries has already leveled off and even started a decline. Q1. Please list down four factors that are said to be causes for a decline in the world capture fisheries. Q2. What management measures do you think should be taken to reverse the situations?

In order to reverse the declining trend of capture fisheries production proper management actions need to be implemented. For instance, fishing of the species and water bodies already fully or over exploited should be avoided for some period of time so that the fish stocks and the environment will regenerate. Otherwise, the effects are damaging not only in terms of socioMulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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economy but also ecologically. Please refer to section 8.2 for better understanding on fisheries management.

Dear student, from Appendix 1 you can see that aquaculture fishery production keeps on increasing in contrast to the capture fisheries. The sector has shown an increasing trend at an increasing rate from 5% per annum in 1950s and 1960s, to 8% per annum in 1970s and 1980s, to 10% per annum in 1990s.

There are some constraints to the sustainability of aquaculture as discussed in section 4.6 of this module. Dear student, please refer to section 4.6 to refresh your memory on the challenges to the sustainability of aquaculture. In spite of all these constraints, it is, however, possible to conclude that aquaculture stands a potential candidate in providing fish supply to human being in the future if it is properly managed.

5.2. Ethiopian Case Details of Ethiopian fisheries have been addressed in chapter 6 of your Aquatic Sciences and Wetland Management (Biol 302) course module. Ethiopia is a landlocked country without maritime access. The country is, however, endowed with about 7000 km 2 wide lakes, 250 km 2 wide reservoirs and ponds, and 7400 km long rivers. Therefore, the Ethiopian fishery comes entirely from inland water bodies (i.e. lakes, reservoirs, ponds and rivers). However, both the capture fisheries and aquaculture sectors of the country are underdeveloped.


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Activity:

Dear students, some basic points about the Ethiopian fisheries have been discussed in chapter 6 of your Aquatic Sciences and Wetland Management Management (Biol 302) 302) course module. From your knowledge of the course: Q. What is an estimate for the Ethiopian capture fishery production potential per year?

Scant and rough studies estimate the country’s annual capture fishery potential to be between 30,000-50,000 tons of fish. There are also reports that indicate the country’s capture fishery potential to be between 44, 00049, 000 tons of fish per year. Despite a little discrepancy in the estimates, it is possible to conclude that the country has a considerable fishery potential that could augment the livelihood of its people if properly utilized. utilized.

Activity:

Dear student, which types of the country’s water bodies (lakes or rivers or reservoirs), do you think that, have the highest capture fishery potential?

Out of the country’s total annual fishery potential 72 % is ascribed to lakes, 15 % to rivers, and 13 % to reservoirs and other small water bodies. Most of the lakes and reservoir fisheries are located in Oromia, Amhara, and Southern Nation Nationalities and Peoples (SNNP) Regions; whereas most of the riverine fisheries come from the Benishangul and Gambela Regions. Activity:

Q. What is an estimate for actual capture fishery production per year from the Ethiopian water bodies?


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The country’s annual average fish production is generally very low despite the crucial need for food supply in the country. For instance, in 1994 only 2528 % of the total fisheries potential was harvested as summarized in Table 5.1. In other words, this means that about 72 - 75 % or 31, 740 – 3 5, 740 tons of the country’s fishery resource has not been still utilized.

Table 5.1. Summary of the Ethiopian fisheries resource potential and actual production for the year 2001/02 (Source: Ethiopian Institute of Agricultural Research, EIAR)

Type of Water body

Production potential

Actual production Tons

Percent

Major Lakes

30,963-35,963

10,441

29-34 %

Major Rivers

7,000

700

10 %

Reservoirs & Ponds

6.067

1, 150

19 %

44,030-49,030

12,291

25-28 %

Total

Activity:

Dear student, we have discussed above that most of the country’s fisheries potential is predominantly attributed to the lakes followed by the rivers. Q. From which of the lakes and rivers do most of the country’s actual capture fisheries come?

Most of the Ethiopian actual Lake fisheries are derived from the rift valley lakes (e.g. Abaya, Chamo, Awassa, Langano, and Zeway) and a high land lake (i.e. Tana Lake), which are located in Oromia, Amhara and SNNP Regions. In contrast, most of the country’s actual riverine fisheries originate from BaroAkobo Rivers in Gambella and Benishangul Regions. Dear student, please refer to chapter 2 of your Aquatic Sciences and Wetlands Management (Biol


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302) course module for the discussion on various lakes and rivers of Ethiopia.

Activity:

Dear student, In our above discussions, we have had a look at the Ethiopian fisheries potential and actual productions from its various inland water bodies. Q. What did the past development activities of the fisheries sector of the country generally look like?

So far some fisheries development projects, under the auspices of mainly the overseas governmental and non-governmental organisations, have been implemented hosted under the Ministry of Agriculture. 

1973 - 1978 : The Japan International Cooperation Agency under

the

Japan

Overseas

Volunteers

Service”

sponsored

the

establishment of the “Freshwater Fisheries Research Station” project, which ultimately established the Fisheries research center located in Sebeta town, near near the capital Addis Addis

Ababa. Dear Dear

student, please refer to section 5.1 of this module for more information on Sebeta Fisheries research center. 

End of 1970s - end of 1980s : The Netherlands based non-

governmental organization (NGO) funded the small scale fisheries development in Gambela, Tana Lake and Arba Minch areas. 

European Union (EU) supported the Lake fisheries development project (LFDP) which was oriented to increase and improve fish production and marketing from the rift valley lakes. LFDP was implemented in two phases: LFDP phase I between 1981 - 1987 and LFDP phase II between 1992 - 1998 .



In 1980s a domestic or national NGO, namely the Ethiopian Orthodox Church/Inter Kerk Urk (EOC/DICA) implemented a


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development project in Lake Tana and southern lakes (such as Chamo and Abaya), which supported a purchase of motorized fishing boats and some equipment.

Activity:

Dear student, we have discussed above about the past development activities of fisheries sector of the county. Q. What do the current state and future prospect of the fisheries sector of the country look like?

In recent times the country has come to recognize the socio-economic benefits of its fishery sector more than ever before. This can be justified by its endorsement of Fisheries Legislation 315/95, which is the first of its kind in the country. Dear student, student, we will come shortly to a brief explanation explanation on the country’s Fisheries Legislation below, and now let’s focus on the sector’s current state and future prospect.

Activity:

Dear student, before we proceed to the discussion on the current state and future prospect of the fisheries sector, can you mention some of the socioeconomic benefits of the sector?

The socio-economic benefits generated from the country’s fisheries sector range from the people’s direct involvement in fishing, construction and supply of fishing gears, and processing and retailing activities, which create additional income and employment to a large number of especially the coastal people. As such the fishery sector, thus, helps in ensuring food security and poverty alleviation particularly to the low income earning


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people. Moreover, due to its high quality nutritional value it helps in preventing deficiency diseases in people consuming fish.

Accordingly, the country has developed a couple of fisheries development projects in recent years. For instance; •

Funded by the African Development Fund (AfDF), in October 2004, a National Fisheries Development Study Project was prepared, prepared, with the main objective of acquiring knowledge on the fisheries resource base, and

identifying

development

and

management

interventions.

However, the status and outcomes of the project have not been reported. •

In April 2009, a National Aquaculture Development Strategy (NADS), funded and supported by the Food and Agriculture Organization SubRegional Office for East Africa, has been prepared. The NADS project has been planned in short-term (2009-2012) and long-term (20102019) bases with the following major objectives: 

Defining a regulatory framework in which the aquaculture industry can be developed in an economically, socially and environmentally environmentally sustainable manner.



Integrating the aquaculture industry into the agricultural sector and to facilitate development of viable aquaculture plans.

The success of these and other projects, and thus the development of fisheries sector of the country, requires commitment of the government and the concerned executive bodies.


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Activity:

Dear student, so far we have discussed about the past and present state, and future prospect of the fisheries sector of the country. We have also mentioned that the country has endorsed the Fisheries Legislation 315/95. What do you think are the values of endorsing such fishery legislation?

Generally fisheries legislations are required for the management and proper utilization of fisheries resources. In the absence of such legislations, there will be no legal basis to control and manage illegal fishery activities and practices. Thus, Ethiopia, Ethiopia, cognizant of the socio-economic socio-economic benefits benefits of its fisheries sector, has endorsed a fisheries legislation numbered 315/95 to ensure proper management and utilization of its fisheries resources.

The Ethiopian fisheries legislation comes in many articles and sub-articles. For instance the legislation in its article 5 and sub-articles 10, 11 and 12 stipulates that: •

Anyone who seeks to import or export live fish into or out of the country should get prior letter of permission from the Minister office (Sub-article 10).

•

Anyone who seeks to introduce an imported or local live fish into the water bodies of one Region into another Region should get prior letter of permission from the Minister office ( Sub-article 11).

•

Anyone who seeks to introduce live fish from a water body of one Region into another water body of the same Region should get prior letter of permission from the concerned regional office ( Sub-article 12).

Dear student, according to the legislation any violation of these regulations will lead to penalty in terms of specified amount of money, imprisonment or both.


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1. What is the current status or trend of capture fisheries production in the world? 2. What is the current status or trend of aquaculture production in the world? 3. What factors could be related to the current status or trend of capture fisheries production in Ethiopia? 4. What is the capture fisheries production potential of Ethiopia? 5. What is the actual fisheries production potential of Ethiopia? 6. List and discuss the past development history of Ethiopian capture fisheries 7. Explain the current development status of Ethiopian fisheries. 8. Discuss some important points about the Ethiopian Fisheries Legislation.


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Benefits of Fisheries Chapter Outline 6.1. Nutrition and Socio-economic Benefits of Fish 6.1.1. Subsistence Fishing 6.1.2. Industrial and Recreational Fishing


Explain the nutritional values of fish diet (proteins, fatty acids, vitamins and minerals)



Discuss the socio-economic benefits generated by the fishermen in general and by the Ethiopian fishermen in particular



Discuss the contribution of industrial and recreational fishing to the countries’ economy.


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6.1. Nutrition and Socio-economic Benefits

Activity:

Dear student, in section 3.1 of this module we have defined the various types of capture fisheries such as subsistence fishing, artisanal fishing, small scale commercial fishing, industrial fishing, recreational fishing, etc. Please go back to the section and try to write down the definition of each in your note book before you go on reading the following sections. 6.1.1. Subsistence or Artisanal Fishing

Subsistence or artisanal fishing primarily provides a nutritious fish diet particularly to the poor society. Therefore, fishes caught through these forms of fishing are virtually used for domestic or local consumption. Moreover, these fishing practices also generate so many socio-economic benefits to the fishermen. These include income and employment secured through gear construction, fish processing, transportation and retailing. Therefore, these fishing activities play a very crucial role in supporting food security in the face of the nations’ population explosion particularly in developing countries like Ethiopia. Dear student, let’s now briefly elaborate on the nutritional values of fish and the associated socio-economic benefits.

Activity:

Dear student, Q1. When we talk about the importance of subsistence fishing as a source of food especially to the poor, does it merely mean to fill up the empty stomachs that couldn’t otherwise afford beef or lamb? Q2. How does the nutritional value of fish compare with that of beef or other types of meat?


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Fish is highly nutritious. It provides proteins, fats, vitamins and minerals. It is evident that fish contribute more to people’s diets than just the high quality protein they are so well known for. Fish should, therefore, be an integral component of every one’s diet, preventing malnutrition by making these macro- and micro-nutrients readily available to the body.

Fish proteins are easily digestible and are of high biological values. On a fresh-weight basis, fish contains a good quantity of protein, about 18-20%, and

contains

all

the

eight

essential

amino

acids

including

the

sulphur-containing lysine, methionine, and cysteine. Thus, fish can complement diets such as maize and cassava that are poor in protein. The fat content of fish varies depending on the species as well as the season but, in general, fish have less fat than red meats. The fat content ranges from 0.2% to 25%.

Activity:

Dear student, Q1. What kind of fatty acids are contained in fish fat? Q2. What are the biological roles of fish fatty acids? Do they have any side effects on human body if consumed?

Fish fats contain the polyunsaturated fatty acids (PUFAs) namely eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These are omega-3 fatty acids which are essential for proper growth of children and are not associated with the occurrence of cardiovascular diseases such as coronary heart disease. In other studies, omega 3 fatty acids have also been associated with reduced risk of pre-term delivery and low birth weight. Moreover, in pregnant women, the presence of PUFAs in their diets has been associated with proper brain development among unborn babies. Fish fat Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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also contributes to energy supplies and assists in the proper absorption of fat soluble vitamins namely A, D, E, and K.

Activity:

Q1. Does fish contain vitamins that are important for proper functioning of human body? Q2. If yes, what are those vitamins and their biological roles? How do they compare with the vitamins obtained from plants? Fish is a rich source of vitamins , particularly vitamins A, B1 (thiamin), B2 (riboflavin), B3 (niacin), D, as well as C (if eaten fresh). Vitamin A is mainly found in fatty fish and is more readily available to our body as compared to that obtained from plant. Vitamin A is required for normal vision and for bone growth. Studies have shown that mortality is reduced for children less than five years of age with a good vitamin A status. As sun drying destroys most of the available vitamin A better processing methods are required to preserve this vitamin. Vitamin D present in fish liver and oils is crucial for bone growth since it is essential for the absorption and metabolism of calcium. Vitamins B1, B2 and B3 are important for energy metabolism. Vitamin C found in fresh fish is important for proper healing of wounds, normal health of body tissues and aids in the absorption of iron in the human body.

Activity:

Q1. Does fish contain minerals that are important for the proper functioning of human body? Q2. If yes, what are the minerals found in fish and their biological roles?

The minerals present in fish include iron, calcium, zinc, iodine (from marine fish), phosphorus, selenium and fluorine. These minerals are highly


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‘bioavailable’ i.e. they are easily absorbed by the body. Iron is important in the synthesis of hemoglobin in red blood cells which is important for transporting oxygen to all parts of the body. Iron deficiency is associated with anemia, impaired brain function and in infants is associated with poor learning ability and poor behavior. Due to its role in the immune system, its deficiency may also be associated with increased risk of infection. Calcium is required in bone formation and making bones strong, and for the normal functioning of muscles and the nervous system. It is also important in the blood clotting process. The intake of calcium, phosphorus and fluorine is higher when small fish are eaten with their bones rather than when the fish bones are discarded. Deficiency of calcium may be associated with rickets in young children and osteomalacia (softening of bones) in adults and older people. Fluorine is also important for strong bones and teeth. Zinc is required for most body processes as it occurs together with proteins in essential enzymes required for metabolism. Zinc plays an important role in growth and development as well in the proper functioning of the immune system and for a healthy skin. Zinc deficiency is associated with poor growth, skin problems problems and loss of hair among other problems. problems. Iodine, present present in seafood, is important for hormones that regulate body metabolism and in children it is required for growth and normal mental development. A deficiency of iodine may lead to goiter (enlarged thyroid gland) and mental retardation in children.


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Activity:

Dear student, we have discussed above about the nutritional values of fish. Let’s now come to the discussion of how people generate income and employment from the various aspects of subsistence or artisanal fishery. Q. Before you proceed to reading the following sections on this topic, can you please think of the various ways people secure income and employment from subsistence or artisanal fishery?

Nowadays, modern gears based on synthetic string and netting are manufactured in factories, and are readily available in most areas of the world. However, traditional gears constructed by local fishermen become important where the modern gears are not available. Therefore, the fishermen or their families can secure income and employment from such traditional gear construction in such instances.

Activity:

Dear student, Q1. After the fishes are caught from the water body, what are the subsequent major activities to be accomplished until the fishes arrive in the hands of the final consumer? Q2. How do these activities benefit various stake holders involved in the process of fishing?

As described in chapter 7 of this module, the major activities need to be accomplished following fish catch, until the fishes are supplied to the final consumer, include processing, transportation and retailing. All these processes create job opportunities for larger number of people depending depending on the scale of fishery.


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6.1.2. Industrial and Recreational Fishing

The values of industrial or large scale commercial fishing extend beyond the food, income and employment benefits generated at the subsistence or artisanal fishing scale. The fishes caught through industrial fishing are processed into various products (see chapter 7 of this module) for export to international market in order to generate income that contributes to the national Gross Domestic Product (GDP). Moreover, the development of recreational fishing attracts tourists and thus generates a tourism industry which will also add to the t he national economy.


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1. How are fish proteins nutritionally important to human being as compared to proteins obtained from other sources? 2. How is fish nutritionally important to human being as compared to fats obtained from other sources? 3. How are vitamins and minerals in fish diets important to human being? 4. List down the various socioeconomic benefits of fisheries 5. Discuss the role of fisheries in improving improving food security


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Processing and Products of Fish Chapter Outline 7.1. Fish Processing Methods 7.1.1. Post-mortem Changes and Fish Quality 7.1.2. Processing Methods 7.1.2.1. Preliminary Processing 7.1.2.2. Main Processing Stage 7.2. Types of Fish Products


Discuss the post-mortem changes that affect fish quality



Distinguish between the preliminary and main fish processing stages



List down the preliminary preliminary fish processing methods



List down the various methods of fish preservation



List down some of the fish products


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7.1. Fish Processing Methods

7.1.1. Post-mortem Changes and Fish Quality

Fish and fish products are fast deteriorating or perishable materials. The easy deterioration in fish quality is because of the post-mortem (after death) biological changes that take place in the body of dead fish. Therefore, fish and fish products need appropriate processing procedures in order to prevent deterioration which would otherwise pose public health risks. Changes in fish quality often come in the form of unpleasant odour and microbial spoilage. We shall come to the discussion of fish processing methods in section 7.1.2.

Activity:

Dear student, can you mention some of the post-mortem biological changes that take place in fish tissue causing it (the fish) to easily perish?

Post-mortem changes that take place in fish tissue occur in the following phases: slime secretion on the surface of fish, rigor mortis, autolysis as enzymatic

decomposition of tissues, microbiological spoilage. The duration of each phase can change or phases can overlap. This depends on storage conditions, especially the temperature which greatly influences these processes.

Activity:

Dear student, now we are going to discuss how an increased slime secretion by fish after death makes fish easily perishable. Before that can you define what slime is?


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Slime is a mucous or thick sticky substance secreted by the skin cells of

certain animals including including fish. When fish is alive slime production adds to the survival of the fish by making its body too slippery to be caught by its predators. In fish the process of slime secretion becomes very active just after fish death often producing as much as 2-3% of the fish mass. The post-mortem production of huge amount of slime by fish creates problems during processing and generally leads to fish spoilage. Of course, slime secretion stops with the onset of the second phase of change namely rigor mortis.

ctivity:

Dear student, can you guess how the post-mortem slime production creates problems in fish processing and how it may cause fish spoilage?

Slime contains large amounts of nitrogenous compounds and these provide good nourishment for micro-organisms originating from the environment. Therefore, the slime spoils quickly: first giving an unpleasant smell to the fish, and second opening the way for further and deeper bacterial penetration into the fish.

Activity:

Dear student, Q1. From our above discussion write down two points how postmortem slime secretion in fish can cause a quality change in fish and fish products. Q2. Now, we are proceeding to the second phase of post-mortem change in fish body namely rigor mortis. Can you define what rigor mortis is?


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Rigor mortis is a condition in which muscle fibres become short and tight,

causing fish to become rigid. This occurs as a result of complicated biochemical reactions that take place in fish muscle cells.

Activity:

Q. What do you think is the effect of rigor mortis on the quality of fish flesh?

Dear student, before trying to mention the effects of rigor mortis on the quality of fish, let’s briefly talk about a fish muscle.

Activity:

Do you think that fish muscle differs from that of other vertebrates in some way? How?

The edible flesh of fish is largely a skeletal muscle, which accounts for more than 50 % of the total fish weight. The structure of skeletal muscles of fish is different from that of other vertebrates (e.g. birds or mammals) in that fish skeletal muscles are largely composed of short bundles of muscle fibres or cells called myomeres (Fig 7.1). Myomeres assume more or less a v-shaped appearance and one myomere is separated from another by various connective tissues. This unique structure and thin connective tissue cover of fish muscle give the meat its characteristic soft and easily crumbling texture.


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Myomere Skin

Fig. 7.1. Myomeres in fish muscle structure. Dear student, it is easy to recognize this unique fish muscle structure just by comparing beef meat against fish meat. Please, do it whenever you happen to get beef and fish fleshes and notice the difference carefully. carefully. Therefore, rigor mortis, because of the shortening of muscle fibers or cells, makes fish flesh short and thick. If, for example, the bones are removed prior to rigor mortis the length of the flesh shortens by as much as 30%. Moreover, because of the tightness of the fish muscle, the connective tissues that hold the myomeres together (see Fig 7.1) break apart causing the separation of myomeres from each other, which in turn is a quality defect in fish flesh. ctivity:

Dear student, we have mentioned above the effects of rigor mortis in fish. How do you think that it is possible to avoid or reduce the effects of rigor mortis in fish? The time rigor mortis begins, after fish death, and its duration depend on the fish species (e.g. for carp at 0° C it starts after 48 hours, for perch at 0° C it starts after 24 hours), on the fish catching technique, and on fish temperature. Moreover, unnecessary and rough handling of the fish can shorten the time of occurrence and duration of rigor mortis. Fish put to death just after removal from the water reach a state of rigor mortis later than those fish which died after a long suffering. For instance, in a carp fish put to Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page 89

death just after capture rigor mortis begins after 48 hours (at 0° C), but if the carp dies after a long suffer it sets in after 24 hours (at 0° C).

Activity:

Dear student, in our discussion above, we have mentioned some of the factors that affect the rate of onset and duration of rigor mortis in fish. Q1. Please list down the factors that affect the onset and duration of rigor mortis in fish. Q2. Can you explain how temperature affects the rate of onset and duration of rigor mortis in fish?

Fish body temperature is a decisive factor in the onset and duration of the rigor mortis process in fish. The higher the temperature the sooner it begins and the faster it ceases. This is evidenced by enzymatic reactions whose speed increases with increased temperature. At high temperatures it results in greater changes in proteins, this in turn causing higher loss of tissue juices such as during processing. Usually, the later rigor mortis begins and the longer it lasts, the longer are the storage life of the fish and its use for consumption.

Activity:

Dear student, Q1. From our above discussion of the relationship between temperature and rigor mortis in fish, can you explain how keeping fish in relatively cold temperature increases increases the shelf life of fish? Q2. The next phase of post-mortem changes in fish body is an autolysis. What is it?

Autolysis is the breakdown or decomposition of larger molecules such as

proteins, lipids and carbohydrates under the influence of enzymes up on the fish death. The quality of fish as a raw material for consumption or for Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page 90

processing depends largely on proteolysis, which is the autolysis of proteins. This is because the proteolysis process leads to a decrease in the capacity of tissue to retain tissue juice, resulting in tough texture of the final product. Moreover, the degradation of proteins creates ideal conditions for the growth of spoilage bacteria.

ctivity:

Dear student, Q1. Please write down the two ways in which proteolysis (i.e. autolysis of proteins) affect the quality of fish. Q2. The last stage of post-mortem changes in fish body is microbial decomposition. What materials do microorganisms decompose in fish body?

Microbial (e.g. bacteria) entry into the fish muscle or flesh is facilitated by the by structural changes in the tissue caused by rigor mortis and autolysis. microbiological decomposition Penetration of bacteria into fish tissue and microbiological

begins with autolysis and these processes are practically parallel. However, their rate and intensity strictly depend on the storage temperature. Low temperature strongly inhibits the activity of microorganisms in which case the autolysis process dominates. Microorganisms such as bacteria cause decomposition of proteins and other compounds containing nitrogen, lipids, aldehydes, ketones and lower aliphatic acids. However, the decomposition of nitrogenous compounds occurs much faster than in the case of lipids.

ctivity:

Q. Freshwater fish tissues undergo microbiological decomposition more slowly than the marine fish tissues. Can you explain why?


Page 91

Bacteria decompose proteins into smaller or low-molecule products such as amino-acids and other low-molecule nitrogenous compounds, which in turn provide nourishment to the bacteria. Thus, due to the lower content of these substances, in freshwater fish tissues microbiological decomposition occurs more slowly in freshwater species than in marine fishes.

Activity:

Dear student, Q1. Why do you think that a microbially spoiled fish may have unpleasant flavor? Q2. Both microbial decomposition and autolysis processes cause the breakdown of fish macromolecules such as carbohydrates, proteins and lipids. So, what is the difference between the two processes?

Compounds such ammonia, hydrogen sulphide, indole, skatole, etc, are the final products of microbiological spoilage of fish, which produces an unpleasant and disgusting flavour. Although both autolysis and microbial decomposition cause the decomposition or breakdown of fish tissue, the former is caused as a result of enzymatic action whereas whereas the latter is because of the action of microorganisms.

7.1.2. Processing Methods Fish processing refers to the processes associated with fish and fish products from the time fish are caught or harvested, from capture fisheries and/or aquaculture, to the time of the delivery of the final product to the end user. Fish is a highly perishable food which needs proper handling and preservation if it is to have a long shelf life and retain a desirable quality and nutritional value. The central concern of fish processing is to prevent fish from deteriorating.


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Activity:

Dear student, fish processing generates wastes often known as fish offal. How do you think that fish offal can be managed to prevent environmental environmental pollution?

Fish wastes (offal) generated from fish processing should not be just dumped into the environment. Fish wastes can be managed by converting them in to byproducts (secondary products) such as fish oil and fishmeal. Fish oil is a healthy

diet for human being because it contains the omega-3 fatty acids including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) that reduce inflammation throughout the body. Fish meal is used as a high-protein supplement in aquaculture feed to rear carnivorous fishes. Dear student, the whole fish processing procedures can be divided in to two major phases: preliminary processing and the main processing stage. We shall see these two phases or stages one after the other.

Activity:

What are the activities or procedures to be accomplished in the preliminary fish processing stage?

7.1.2.1. Preliminary Processing This stage is also referred to as pre-processing stage in some literature. Preliminary processing of fish usually consists of grading, removal of slime, deheading (also called beheading), scaling, washing, cutting of fins, gutting and evisceration, slicing of whole fish into steaks, skinning, filleting, grinding of skinned fillets, meat-bone meat-bone separation, separation, and various combinations combinations of these. Some of these procedures are shown in Fig. 7.2.


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Fig. 7.2. Some of the pre-processing procedures procedures in fish processing

Activity:

Dear student, can you define the terms mentioned above in preprocessing stage of fish and fish products?

Definitions of some of the terminologies which may not be explicit are given below: 

Grading refers to the sorting of fishes according to certain criteria such as by species or size.



Deheading (beheading) refers to the cutting and removal of head using a sharp knife.



Scaling refers to the removal of scales. This can be done manually using knife.


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

Skinning refers to the removal of skin from the flesh. This can also be done manually and easily using a sharp knife.



Gutting and evisceration refer to the removal of gut content



Filleting is preparation of fillet, which is a bone free flesh of fish.

7.1.2.2. Main Processing Stage This phase or stage is mainly concerned with fish preservation processes. Microorganisms particularly the spoilage bacteria require appropriate temperature, sufficient water and oxygen, and less acidic environments to reproduce and multiply. Thus, the various techniques used in fish preservation are based on the principles of interrupting these conditions as summarised in Table 7.1. In fish preservation we often use combinations of these methods. Table 7.1. Summary of fish preservation methods and parameters controlled Parameter to be controlled

Method used

Temperature Temperature

Chilling, Refrigeration, Refrigeration, Freezing

Water activity

Smoking, Freeze-drying Freeze-drying

Oxygen

Vacuum pumping

Chemical control of microbes (pH)

Addition of acids

Physical control of microbes

Microwave heating, Ionizing

Dear student, among the various methods of fish preservation summarised in Table 7.1, we will only briefly discuss below some of them. t hem. Chilling, Freezing and Refrigeration

These are preservation methods that involve temperature control. In all the three methods temperature is decreased in order to reduce the metabolic activities that take place in the fish due to autolytic or microbial processes (see section 7.1.1). Moreover, these methods make water less available for bacterial


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growth thereby slowing the growth of microorganisms. In chilling and refrigeration the temperature drops to about 0 °C whereas freezing drops the temperature to below -18°C. Therefore, differences among the three methods lie on the materials used: ice box for chilling, refrigerators for refrigeration and deep freezers for freezing. Thus, fish should be quickly kept at low temperature

immediately after capture or harvest, during transport, processing and distribution. Fish and fish products are often transported frozen. However, it should be accompanied by insulated containers or transport vehicles and adequate refrigeration to ensure safety. Drying and Smoking Drying is a process of removing water from the food in order to inhibit the

growth of microorganisms. Microorganisms such as bacteria and moulds need the water in the food to grow. Thus, drying effectively prevents them from surviving in the food. Water is usually removed by evaporation (air drying, sun drying, smoking or wind drying) but, in the case of freeze-drying water is removed by sublimation after food is first frozen. Smoking is done by exposing fish to the smoke from burning or flaming wood (Fig 7.3b). It not only preserves fish but also helps in flavoring and cooking. Therefore, it comes in different forms such as cold smoking and hot smoking. In cold smoking fish is exposed to temperatures below 38 °C. It thus helps mainly in flavouring; but does not cook foods. In hot smoking fish is exposed to a temperature range of 74 °C-85 °C. Within this temperature range, foods are fully cooked, moist, and flavorful. Salting and Pickling

Salting is the preservation of food with dry edible salt. It is related to

pickling (i.e. preparing food with salty water). Salting is used to inhibit the growth of microorganisms including most bacteria and fungi by creating a highly salty or hypertonic condition. Pickling (also known as brining or corning) is the process of preserving food by anaerobic fermentation in Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

Page 96

brine (i.e. a solution of salt in water) to produce lactic acid. It creates a pH less than 4.6, which is sufficient to kill most bacteria. Pickling can preserve fish foods for months.

In Canning, processed fish products are sealed or packed in airtight containers called cans (Fig. 7.3a). In canning a tight packing prevents microorganisms microorganisms from getting inside. inside. Canning provides a longer shelf life ranging from one to five years, although under specific circumstances a freeze-dried freeze-dried canned product can last as long as 30 years in an edible state.

Fig. 7.3. (a) Canned fish, (b) Smoked fish

In order to prevent fish spoilage before and during canning various methods are used. These include sterilization using pressure canners, pasteurisation, boiling, refrigeration, freezing, drying, vacuum treatment, addition of antimicrobial agents that are natural to the recipe of the foods being preserved, a sufficient dose of ionizing radiation and submersion (in strong solutions such as saline, acid, base, sugar etc).


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7.2. Types of Fish Products

Activity:

Dear student, from our discussion of fish processing methods above in section 7.1, can you mention or define some of the types of fish products?

Some of the fish products are cooked fish, frozen fish, dried fish, smoked fish, salted fish, canned fish, fermented fish etc.

Cooked fish products are most usually for immediate consumption and

require no sophisticated packaging. The shelf-life can be extended for a few days by using refrigerated storage and the product should be covered to prevent recontamination. Frozen fish products have relatively long-term preservation, preservation, but the technique is relatively expensive in terms of equipment and operating costs. Thus, it is not recommended for the majority of smallscale fisheries.

Cured fish (dried fish, smoked fish and salted fish) products have reduced

water content and thus prevent the development of spoilage bacteria. Canned fish products have much longer shelf life. Fermented fish products

are formed by encouraging the development of bacteria that increase the acidity of the fish so that pH of the fish products is lowered. Low pH discourages the growth of spoilage microorganisms.


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1. List down the post-mortem changes in fish and define each 2. How does each of the post-mortem changes in fishes relate to fish quality? 3. List down and define each of the preliminary fish processing stages 4. List down the various fish preservation methods and how they work 5. List down some of the fish products


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Fisheries Management Chapter Outline 8.1. Stock Assessment 8.1.1. Definitions and Stock Concept 8.1.2. Survey of Stock Population 8.1.3. Quantitative Estimation of Stock Population 8.2. Sustainable Exploitation of the Fisheries Resources


Define stock assessment



Define stock and stock concepts



List down and discuss the various methods of survey of stock population



List down and define the various methods in quantitative estimation of stock population



Define the maximum sustainable yield (MSY)?



List down and discuss the various management measures that can be implemented for sustainable utilization of fisheries resources


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8.1. Stock Assessment

8.1.1. Definitions and Stock Concept

Activity:

Dear student, Q1. What is fish stock assessment? Q2. Why is a stock assessment important in fisheries? Fish stock assessment may be defined as gathering information and estimating parameters related to fish biomass and its population dynamics (e.g. fish growth and age). The information gathered via stock assessment is important in fisheries management system because management measures can be implemented based on such information about fish population and its dynamics.

Activity:

Dear student, Q. What is a fisheries management?

Fisheries management is a science of sustainable exploitation or utilization of fisheries resources. Fisheries management puts forward measures that that need to be implemented in order to sustainably utilize the fisheries resources.


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Activity:

Dear student, Q1. What do we mean by sustainable utilization of resources? Q2.What do you think are the various objectives of fisheries management that require appropriate stock assessment for their achievement?

Sustainable utilization refers to the use of resources without compromising or affecting their future existence. The various fisheries management objectives include: 

Maximizing sustainable fish yield or production from the existing exploited fish stock



Conservation of exploited fish species



Controlling water quality through biomanipulation of fish

Therefore, the importance of fish stock assessment is to provide information on how these fisheries management objectives may be achieved to ensure sustainable utilization. Dear student, please refer to section 8.2 of this module for better details on the fisheries management and sustainable exploitation of fisheries resources. Activity:

Dear student, Q1. What is a “stock” in fisheries management? Q2. How can a “stock” be identified?

The “stock” concept and methods of stock identification are integral part of and a preliminary step in sock assessment. Fisheries assessment and thus fisheries management management are based on small groups of fish population known as a unit stock. There is no unanimous definition of “stock” in fisheries


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management. The concept and definition of fish stock are evolving from the early time.

Details of the stock concept and its definitions in fisheries assessment and management are focus of advanced courses. However, as far as this course is concerned, we may define a unit stock as a discrete or semi-discrete group of fishes that has the same gene pool, is self-perpetuating, inhabits the same geographical geographical area, and has the same parameters of population dynamics (e.g. growth and mortality) over the whole area occupied.

Activity:

Dear student, once we complete the preliminary step in stock assessment i.e. stock identification, what do you think are the subsequent major steps in order to produce a complete information for fisheries management? Next to stock identification any stock assessment process should pass through two major steps to yield complete assessment information for fisheries management. These are: 

Population survey of the stock population



Quantitative estimation of the stock population

8.1.2. Survey of Stock Population

Population survey is a stock assessment phase when all the necessary information or data (e.g. growth, age, mortality, etc) relevant to the stock (s) under consideration are gathered; whereas in quantitative estimation we estimate stock abundance and/or its production based on the collected data.


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Activity:

Dear student, we have mentioned above that there are two major phases or steps in stock assessment. Can you give some examples for each phase?

As we have already mentioned population survey is the first step in stock assessment. The survey techniques or methods used in gathering population information can be catch dependent or catch independent . The catchdependent population survey techniques are based on gathering the population information by catching the fish. This can be accomplished through a planned survey programme to catch fish or by collecting the required information or data from the already existing fishery data.

Activity:

Dear student, Q1. What is the difference between the planned survey and collecting information from the existing fishery data in stock assessment? Q2. Can you give examples for each of these two types of catch dependent dependent population survey methods?

In a planned survey, investigators catch the fish and collect the required information using various techniques such as netting, trolling, trawling, etc. Please refer to section 3.3 of this module for the various fishing or catch techniques. However, in collecting data from the existing catch data, investigators collect information from the record of the already existing capture fishery data. In this case the source of information can be the artisanal or commercial fishery.


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Catch independent method is the second and another technique of population survey in stock assessment in fishery. This method does not involve the catch of fish to gather the necessary information. Activity:

Dear student, can you give one example of such catch independent population survey method in stock assessment?

Catch independent methods of population survey include electronic fish counter, observation and hydroacoustic. However, hydroacoustic survey is the main catch-independent method that is often applied to freshwater bodies particularly lakes and reservoirs. Hydroacoustic, also known as remote sensing, involves the use of an instrument called sonar with an echo sounder and echo-integrator echo-integrator to make an estimation of fish biomass.

ctivity:

Dear student, do you think that there is any difference in stock assessment: (a) in streams and large water bodies? (b) between tropical and temperate regions?

Stock assessment survey is relatively easier in small streams and rivers, and becomes progressively difficult in large water bodies such as deep lakes due to an increase in depth and area that limit the efficiency of the methods being used. Stock assessment methods in temperate and tropical regions tend to be similar except that collecting data appears to be more difficult in the tropics, and poses difficulty in stock assessments methods. For instance, in tropics ageing (i.e. estimating an age) of fish from the hard body parts such as otolith and scales is often difficult because fish growth in tropics is not always sufficiently seasonal.


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Activity:

Dear student, fish ageing is one of the activities in fish population survey to estimate the rate of growth. Can you mention the different methods used to age fish?

Fish age can be estimated from hard body parts of fish such as scales, otolith and bones (e.g. vertebrae or back bones). The age estimation is often based on counting of growth rings from the cross sections of these hard parts that are formed seasonally as fish grows. This is more or less similar to age estimation of large trees from growth rings rings of tree trunk. trunk. Another approach approach for estimating fish age is by length frequency method. In this method the length measurement of large number of fish is taken or recorded and then converted into age using length distribution curves or length-age keys.

8.1.3. Quantitative Estimation of Stock Population

Various methods and models exist for the quantitative appraisal or assessment of fish stock abundance and its yield or production. Activity:

Dear student, can you mention some of the methods or models used in quantitative estimation of fish population abundance and its production?

Some of the methods used in fish stock quantitative assessment include: •

Empirical models

•

Surplus production models

•

Analytical methods (e.g. virtual population analysis and catch curve analysis )

•

Mark-recapture Mark-recapture method

•

Mass removal or depletion methods


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•

Swept area method

•

Catch per unit effort (CPUE) method.

Activity:

Dear student, which of the methods of fish population quantitative assessment mentioned above are used to estimate: (a) potential yield or production of fish population? (b) fish population abundance? abundance? Empirical and surplus production models help to make an appraisal of fish productions or yields; whereas the rest of the methods enable to give an estimation of stock abundance. Activity:

Dear student, which of the methods used in estimating fish stock abundance give absolute and relative estimation of stock abundance?

Catch per unit effort (CPUE) measures the relative change in population abundance; whereas the rest of the methods measure the absolute fish abundance.

Dear student, it is, however, important to note that these quantitative methods of estimating fish production and abundance are associated with certain limitations. For instance, •

They all are based on assumptions that may not be always achieved. Therefore, the reliability of any single method becomes questioned.

•

Some of the methods such as surplus production and analytical models are costly because they need long time series data.

Thus, when we do quantitative appraisal of fish stock population, it is advisable to use combinations of methods to increase reliability of the results. Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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Activity:

Dear student, why do you think that the result of quantitative estimation of fish population should be as genuine as possible?

The results of stock assessments are used for planning appropriate management measures to ensure sustainability of fish resources or for biodiversity conservation. Thus, if the results of stock assessment are unreliable, wrong management decisions will be made.

8.2. Sustainable Exploitation of Fisheries Resources

Ensuring sustainable fisheries exploitation is a sole job of fisheries management. management. As discussed in Chapter 5 of this module most of the natural or capture fisheries from the major water bodies have already leveled off due to overfishing.

Activity: Dear student, what do we mean by overfishing?

Overfishing, i.e. fishing beyond the maximum sustainable yield, is the major threat that has caused the natural or capture fisheries to peak off in most of the natural water bodies.


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Activity:

Dear student, what do we mean by the maximum sustainable yield (MSY)?

Maximum sustainable yield in fisheries may be defined as the level at which fisheries resources can be exploited without exhausting them. This is demonstrated in a simple fishery bioeconomic model given in Fig. 8.1. Any fishing effort exerted up to the point of the maximum sustainable sustainable yield (MSY) is biologically sustainable. In contrast, any fishing effort that goes beyond the MSY is unsustainable as can be seen from Fig. 8.1. Dear student, please carefully look at Fig. 8.1. As fishing effort is increased beyond the MSY, production starts to decline indicating that any fishing activity beyond the MSY causes the fishery resources to exhaust.

Fig. 8.1. A Simple Bioeconomic Fishery Model. After Karagiannagos (1995).


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Activity:

Dear student, we have seen above that overfishing is the major threat to sustainable utilization of fisheries resources. What different management measures do you think need to be implemented in order to ensure sustainability of the fisheries resources?

The various management measures that can be implemented in order to prevent overfishing and thus to ensure sustainability of fishery resources include: •

Limiting the efficiency and types of fishing gear

•

Closures

•

Size limits

•

Rejection of spawning females

Activity:

Dear student, can you explain how each of the above mentioned management measures can be used to ensure sustainability of the fisheries Catch resources quotasby preventing overfishing? overfishing? •

A. Limiting the Efficiency and Types of Fishing Gear

Dear student, at this point you should be able to refresh your memory on the various types of fishing gears discussed in chapter 3 of this module.

In fisheries management, the use of fishing gears can be limited in number, type and size, and some highly efficient or destructive fishing gears and methods can be banned altogether. For instance, it is possible to restrict the minimum mesh size of gillnet in order to limit the smallest possible size of fish to be caught. Setting or limiting the smallest allowable mesh size


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prevents the catch of undersize or young fishes and allows the catch of larger size fishes.

ctivity:

Dear student, although gear restriction is a useful management strategy, it often is associated with some constraints. Can you mention any limitation associated with gear restriction in fisheries management? management?

Fishing gear restriction usually leads to fishing inefficiency and thus raises the cost of catching fish particularly in large scale or industrial fishing. Thus, gear restriction as a management strategy can be more applicable in small scale or artisanal fishing. It, however, puts the large scale commercial fishers at disadvantage. B. Closures

In fisheries management closures refer to restrictions of either fishing season or fishing areas. Restriction of fishing season is called temporal closure, which is a particular time period or season when fishing is prohibited. Restriction of fishing area is known as spatial closure, which is avoiding fishing of a particular part or area of a water body.

Activity:

Dear student, how does the temporal closure help in fisheries management?

Dear student, please refer to chapter 2 of this module and refresh your memory on recruitment and spawning before you read the following paragraph.


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If the period of recruitment of a particular species of fish is short and well defined, enforcing temporal closure during the time of recruitment allows small or young individuals to grow to marketable size. Similarly closed seasons during well defined spawning period can allow adults to breed without interference. interference.

Activity:

Dear student, how does the spatial closure help in fisheries management?

Spatial closure can be imposed in nursery and spawning grounds. Identifying nursery areas, usually the shore areas where the juvenile or young fishes are fed and grown up, and enforcing no fishing in such areas, can help protect the juveniles from early fishing. Similarly, if spawning areas are properly identified and fishing activities are banned or prohibited, the reproducing adults are protected. Temporal and and spatial closures closures can be implemented implemented separately or in combination; the overall effect of closures being an increase in the total fish catch depending on other factors. C. Size Limits

Limiting the size of individual retained in a catch during fishing is enforced through regulations. The regulation involves returning captured individual smaller than a prescribed minimum size to water body.

D. Rejection of Spawning Females

This method involves returning females or egg bearing females to the water body but it may not be always applicable especially to in fast growing species with high fecundity.


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1. What is a fish stock? 2. What is a fish stock assessment? 3. Why is stock assessment important in fisheries? 4. What are the various methods used to survey s tock populations? 5. What are the various methods used in quantitative estimation of stock population? 6. What is the maximum sustainable yield (MSY)? 7. What are the various methods or strategies used to ensure sustainable exploitation of fisheries resources?


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Fish Parasites and Diseases Chapter Outline 9.1. Fish Immunity 9.2. Major Fish Parasites 9.2.1. Protozoan Parasites of Fishes 9.2.2. Helminthic Parasites of Fishes 9.2.2.1. Platyhelminthic Parasites of Fishes 9.2.2.2. Nematode Parasites of Fishes 9.2.2.3. Annelid Parasites of Fishes 9.2.2.4. Acanthocephalan Parasites of Fishes 9.2.3. Copepod Parasites of Fishes 9.3. Major Fish Diseases 9.3.1. Bacterial Diseases of Fishes 9.3.2. Viral Disease of Fishes 9.3.3. Fungal Diseases of Fishes


Distinguish between the specific and non-specific fish immune system



List down the major groups of fish parasites (protozoan, helminthic, copepod or arthropod, bacterial, viral and fungal parasites)



Give examples of each major group of fish parasite



Describe the life cycle and infective stage of some of the important fish parasites



Give examples and effects fish bacterial, viral and fungal diseases


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9.1. Fish Immunity

The body defense of fishes has a variety of both non-specific and specific immune system. The non-specific defense system comprises the skin and scales, as well as the mucus or slime layer secreted by their skin epidermis.

Activity:

Dear student, Q1. How are the fish skin, scale and mucus secretion important in fish immune system? Q2. Why is a fish defense comprising of these structures called “nonspecific”?

Non-specific immunity is comprised of defenses that combat a variety of pathogens at one time rather than a single microbe. Skin and scale cover the fish body externally like our (human) body is covered with skin. Therefore, fish skin and scale give primary protection by preventing direct entry of disease causing organisms into the fish body. Mucus or slime is important in trapping microorganisms and inhibiting their growth.

Activity:

Dear student, next we are going to discuss about the non-specific immune system of fish. How do you think that this is different from the specific immune system?

Unlike the non-specific defense system, specific defense involves specialised responses to particular particular pathogens pathogens recognised by the fish's body. body.

For

instance, fish can develop an inflammatory response that increases the flow of blood to the infected region and delivers delivers white blood cells (WBCs) that will attempt to destroy the pathogens. In recent years, vaccines have become widely used in aquaculture and also with ornamental fish. Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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Activity:

Dear student, now we will proceed to the discussion on fish parasites. Q1. What is a parasite? Q2. Can you list down some of the major groups of fish parasites?

9.2. Major Fish Parasites A parasite is an organism that lives in or on another larger organism of a different species (the host), upon which it depends for food and shelter. In host-parasite relationship, relationship, the parasite benefits from the association whereas the host is harmed.

Activity:

Dear student, Q1. Do you expect fish parasites and diseases to me a main problem in aquaculture or in natural environments of fish? Why? Q2. What do you think are the various effects of fish parasites to their fish hosts?

Fish parasites and diseases are more usually common in aquaculture or fish farming ponds than in the natural fish environments. This is because of the increased stress to the fish due to their confinement to small area in the former whereas fishes can disperse over wide area in the latter reducing stress. Therefore, as we shall see later in the subsequent sections, treatment of fish parasites and diseases often apply to the aquaculture settings.

Depending on the species, the host-parasite relationship may be temporary or permanent. Parasites generally do not kill their hosts, but some can Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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severely stress fish populations to the point of becoming biological and economical concerns. The effects caused by fish parasites include destroying fish tissue, removing fish blood and cellular fluids, diverting part of fish nutrient supply and allowing secondary infections to develop in fish body.

Activity:

Q1. Do you think that fish parasites are communicable to human being? Q2. If yes, what do we call such a transfer of parasites from animals such as fish to humans? Q3. What is the difference between the terms parasite infection and infestation? The transfer of parasites from animals such as fish to human is known as zoonosis . Almost all fishes have parasites but only very few fish parasites

can be transferred to humans. Even when a fish exhibits obvious signs of disease or parasites, most likely the fish is still edible when cooked, hot smoked, or frozen. People, however, could be infected with tapeworms (Diphyllobothrium latum) after consuming marinated, uncooked fish. Infection is caused by parasites that get into the host (fish) body (e.g. fish

tape worm) whereas infestation is caused by parasites that inhabit the external or superficial body parts (e.g. fish lice).

Dear student, fish parasites come from all the known parasite groups as summarized in Table 9.1.


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Table 9.1. The Major Groups of fish Parasites

Major Groups

Protozoa

Subgroups

Ciliates

Flagellates

Genus/Common name examples

Ichthyophthirius, Chilodonella, Tetrahymena, Trichodina, Ambiphyra, Apiosoma, Epistylis, Capriniana Ichthyobodo, Hexamita, Spironucleus, Piscinoodinium, Cryptobia

Myxozoa Microsporida Coccidian Monogenic flukes (Dactylogyrus,

Platyhelminthes (Flatworms)

Gyrodactylus and Benedeniella); Digenic flukes (Clinostomum and Uvulifer ); ); Cestodes (Protcephalus, Diphyllobothrium and Ligula )

Helmithes (Worms)

Arthropods

Nematodes (Roundworms)

Camalanus, Capillaria, Contracaecum Contracaecum

and Eustrongyloides

Annelids (True worms)

Leech

Acanthocephalans Acanthocephalans (Spiny headed worms) Copepods (Crustaceans)

Argulus, Ergasilus and Lernaea

Viruses Bacteria Fungi

Dear student, owing to the time restriction to discuss all the various parasites, we will restrict ourselves to one or a few typical examples.


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9.2.1. Protozo n Parasites of Fishes (e.g. Ciliates)

Among the ciliate s Ichthyophthirius multifiliis is the most commonly encountered fish parasite. It i a single-celled protozoan parasite that can i fest virtually all freshwater fish in cluding both cold water and tropical species. It causes a disease called known as white spot disease (Ich). The term “white s ot” refers to the gross appearance of fish infected with this parasite as in Fig 9.1.

Fig. 9.1. A fish in fested with a ciliated I. multifilis Activity:

Dear student, carefully observe the various fish body pa rts I. multifilis infects. Q1. What are he white spots in I. mulifilis infection of fish? Q2. Which bo y parts of fish does the parasite I. multifilis i fect?

The small white spots are fish body parts that contain the para site ( I. multifilis) beneath and unde r severe infections several spots may coalesce to form irregular Mulugeta Wakjira, Department of Biology, Jimma University, June 2 011,

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white patches. The parasite infests fish body parts such as skin, fins and gills though the white spots may not be seen on gills. The gills rather appear swollen and become covered with thick mucus. Activity:

Dear student, what are the effects of I. multifilis infestation to fish?

The effects of I. multifilis infection include: 

Parasites feed on body fluids and cells



Heavily parasitized fish may have many white spots and often scratch against rocks and gravel, may show increased gill movements.



Development Development of secondary bacterial infections since the slime coat and epithelium of the fish are compromised.

Activity:

From our discussions above about the fish parasite namely I. multifilis, Q1. What is the name of the disease it causes to the infected fish? Q2. What are the effects of I. multifilis infection to fish? Q3. What kind of life cycle c ycle does it have (direct or indirect)?

The life cycle of I. multifilis is direct involving only one species of host. The parasite consists of both the free-living and parasitic stages. These include the mature parasite stage, cysts stage and swarmmer stage. The mature parasites feed on the host tissues (beneath the white spots), break through

the skin and fall away from the fish into water. In water they form the next and free living stage known as cyst. Cyst is Cyst is parasite’s the reproductive stage that divides many times, eventually producing many hundreds of the swarmmers. Eventually, swarmmers get out of the cysts and swim off to find

a fish host to infect. If they find a host fish, they enter into the fish bodies such as skin, scale, fin and gill and gradually develop into the mature parasite Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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stage that causes the development of white spot on the fish body. If they do not find a host within several days, they die. Thus, a swarmmer is the parasite’s infective stage.

Activity:

Dear student, from our above discussion about the life cycle of I. multifilis,

Q1. What does direct life cycle mean? Q2. What are the three stages of development of the parasite I. multifilis?

Q3. Which of the parasite’s stages are free living? Parasitic? Q4. What is the infective stage of the parasite? Q5. What is the mode of transmission of the infective stage of the parasite to the host fish? Q6. What factors do you think may influence the parasite to complete its life cycle?

The mode of transfer of the parasite’s infective stage (swarmmers) to the host fish is a direct entry through penetration. The time required by the parasite to complete its life cycle depends on the water temperature: the higher the water temperature, the faster the life cycle. At low temperatures, the parasite may become dormant for considerable lengths of time.

Activity:

Dear student, what do you think is the possible treatment of the parasite? Most treatments of the parasite are ineffective due to occurrence of the parasite within the fish skin. The various treatment methods of the parasite include immersing the infested fish in chemicals or solutions of differing concentrations such as sodium chloride (salt), formalin (formaldehyde), Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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malachite green, victoria green, acriflavin and copper. In aquaculture systems, the parasite can be introduced with fish, live plants or live food brought from another water body. Thus, prevention methods such as proper quarantine of the infested fish are more important.

9.2.2. Helminthic Parasites of Fishes

As summarised in Table 9.1 the helminthic (worm) parasites of fish belong to four major subgroups. We will discuss only a few representatives from each subgroup.

9.2.2.1. Platyhelminthic Parasites of Fishes These are commonly known as flat worms due to their dorso-ventrally flat appearance. The parasitic flat worms of fish belong to two major subcategories namely flukes (trematodes) and cestodes (tape worms). Dear student, we will discuss briefly about the fish flukes (A) and cestodes (B) below. A. Flukes (Trematodes)

These are also known as trematodes and are categorized into two subgroups as monogenea and digenea.

Activity:

Dear student, what are the major differences that exist between these two subgroups of flukes: monogenean and digenean?


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Table 9.2. Comparison and contrast between monogenic and digeneic flukes

Character Mode of parasitism Attachment organ

Monogenea Mainly ectoparasites

Digenea Mainly endoparasites endoparasites

Series of hooks (see Fig. 9.2)

Life cycle

Direct (only one species of host is required) Direct transfer from fish to fish Bathing fish in solutions of praziquantal, praziquantal, Trichlorofon or salt Dactylogyrus, Gyrodactlylus, Gyrodactlylus, Benedeniela

Two suckers: oral and ventral suckers (see Fig. 9.3) Indirect (≥ 2 species of hosts are required) Penetration and ingestion

Mode of transmission Treatment

Genera Examples

Bathing in praziquantal solution Clinostomum and Marginatum

Dear student, hereunder we will briefly discuss about the monogenic and digenic flukes. We will begin our discussion with monogeneans and then proceed to that of the digenic flukes.

Activity:

Q1. Which of the three genera examples of monogenetic flukes given in Table 9.2 are parasitic to (a) freshwater fishes, (b) marine fishes? Q2. What is the difference among the three parasites in terms of their development development and developmental stages?


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Hooks for attachment

Fig. 9.2. The three genera examples examples of monogenic flukes

Dactylogyrus and Gyrodactylus are mainly parasitic to freshwater fishes while Benedeniella is a parasite of marine fish species. The parasites are

hermaphrodites having both male and female reproductive organs. Dactylogyrus is an oviparous (i.e. egg layer) and thus has three

developmental stages consisting of egg, larva and adults. Whereas Gyrodactylus is viviparous (i.e. gives birth to live young or larva) and thus has

two developmental stages: larva and adults.

Activity:

Dear student, what do you think are the clinical signs and effects of fishes infected or infested by these monogenic flukes?

Freshwater fish infested with skin-inhabiting flukes become lethargic or sluggish, swim near the surface, seek the sides of the pond and their appetite dwindles. They may be seen rubbing the bottom or sides of the holding facility (flashing). The skin, where the flukes are attached, shows areas of scale loss and may ooze a pinkish fluid. Heavy gill infestations result in respiratory disease. Gills may be swollen and become pale, respiration rate may be increased, and fish will be less tolerant of low oxygen conditions. Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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Gulping air at the water surface may be observed in fishes with severe respiratory distress. Large numbers of monogeneans on either the skin or gills may result in significant damage and mortality. Secondary infection by bacteria and fungus is common on tissue that has been damaged by monogeneans.

Activity:

Dear student, Q1. What is the infective stage of monogenan flukes to (a) fish, (b) human? Q2. What is the mode of transmission of the parasites from (a) fish to fish, (b) from fish to humans? Q3. What are the public and socio-economic impacts of fish infested by these parasites?

The larval stage of the monogenic flukes is transmitted from fish to fish via body penetration. The larval stages invade the superficial fish tissues such as skin, fin and gills and develop into the adult stage. Then, adults of Dactylogyrus shed eggs to be discharged into the water and hatch into larva;

whereas adults of Gyrodactylus give birth to live larva that will also enter water in search of another fish host as we have already discussed above. The possibility of the parasite being acquired by humans is rare since these parasites occupy fish tissues such as skin that can be easily avoided through proper skinning. Thus, the public health concern is less important but the parasites may cause economic loss in aquaculture systems by causing damage to fish health.

Dear student, we will now discuss some important points about the digenean digenean flukes. The suckers used by the parasite for attachment during feeding on the host tissue are shown in Fig. 9.3.


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Ventral sucker

Oral sucker

Fig. 9.3. An adult digenean fluke

Activity:

Dear student, Q1. Can you give some examples of digeneic flukes? Q2. How many species of hosts are required by each of these digenic parasites to complete their life cycles? Q3. What is the difference between the definitive host and intermediate intermediate host? Q4. What are the stages of development for each example of digenic parasite?

The two common examples of the digenean flukes are Clinostomum marginatum (commonly known as yellow grub) and Uvulifer ambloplitis

(commonly known as black grup or spot). Both parasites have indirect life cycle as shown in Fig. 9.4 for the C. marginatum.


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Fish, Definitive host

Heron, Intermediate host

Snail, Intermediate host

Fig.9.4. Life cycle of Clinostomum marginatum (yellow grub)

Three species of hosts are required by both parasites to complete their life cycles. These are fish, birds (e.g. heron) and mollusk (snail). Fish is a definitive host whereas bird and snail are the intermediate hosts. The developmental developmental stages of both parasites consist of adult , egg and three larval stages known as miracidium (1st larval stage), cercaria (2nd larval stage)

and metacercaria (3rd larval stage). The larval stages may be encysted i.e. found in the cyst form.

Adult digeneans are usually found in the gastro-intestinal tract (GIT) such as mouth, throat, esophagus and intestine of their hosts; whereas the larval stages can be found in various host tissues and cause problems if they invade such organs as the eyes or heart in high numbers.


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Activity:

Q1. Which of the fish tissues do you think are invaded by the larval stages of the fluke parasite C. marginatum?

The larval stages of the parasite are found as whitish or yellowish cysts in the flesh and near or just beneath the skin of fish, especially at the base of the fins and tail.

Activity:

By referring to the life cycle of C. marginatum diagrammatically represented in Fig. 9.4., Q1. Can you identify the definitive and intermediate hosts? Q2. Can you identify the various stages of the parasite? Q3. Can you identify the modes of transmission of the parasite to the various hosts?

•

The adult C. marginatum are found in the mouth, under tongue, in the throat and esophagus of fish eating birds such as heron. Heron serves as the first intermediate host to the parasite.

•

The adult parasites thus shed their eggs into water when the birds feed in the water.

•

Very soon the eggs hatch into the actively swimming first larval stage known as miracidium.

•

Miracidium continues to swim actively in the water until it will find a second intermediate host, which is a mollusk known as snail. When miracidium encounters encounters a snail, it enters the snail by penetrating the body.


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Activity:

Dear student, Q1. From the above discussions, what is the mode of transfer of miracidium to the second intermediate host (snail)? Q2. What is the infective stage of the parasite C. marginatum to the intermediate intermediate host (snail)?

The mode of transfer of miracidium to the second intermediate host (snail) is through penetration. Thus, miracidium is an infective stage of the parasite to the second intermediate host (snail). •

Within the body of the snail the first larval stage i.e. miracidium develops into the second larval stage called cercaria. Cercaria leaves or gets out of the snail’s body again through penetration. After leaving the snail’s body, the cercaria then swims freely in the water until it will find a fish host, which is a definitive host of the parasite.

ctivity:

Dear student, Q1. What is the infective stage of the parasite to the definitive host (fish)? Q2. What is the mode of transfer of the parasite to the definitive host (fish)?

•

The second larval stage of the parasite, cercaria, is infective to the definitive host (fish). It gets into the definitive host (fish) by penetrating the body. After penetrating into the body of fish, cercaria develops into the third larval stage known as metacercaria that encysts in fish internal organs (such as liver and muscle) or in external tissues (such as fin, skin and gill).


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•

When the infected fish is eaten by a bird such as heron, metacercaria is transmitted to a bird to become adult, and the cycle continues. Thus, the mode of transmission of the parasite to the first intermediate host is through ingestion.

•

Once ingested by the bird, metacercaria metacercaria develops into the adult stage that stays in the bird’s GIT such as mouth and esophagus. The parasite ultimately gets back to the water when adults discharge their eggs as described above. Activity:

From our above discussions about the life cycle of C. marginatum, what can you infer about the public health and socio-economic impacts of fish infected by this parasite? The parasite (metacercaria stage) is transmitted to human being when fish is ingested or consumed. However, zoonotic infection cases are generally rare because the parasite can be avoided via proper skinning if the parasite (metacercaria stage) occupies the external tissues such as skin; and if the parasite (metacercaria stage) occupies the internal tissues such as muscle it can be prevented by eating well cooked fish. Thus, there is no serious public health concern; economic concern is rather more important. That is because the infection makes fish unmarketable for aesthetic reasons i.e. due to the bad appearance of fish infected by the parasite.


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Activity:

Dear student, so far we have discussed about the life cycle of the digenean fluke parasite known as C. marginatum. From our discussions, Q1. What is the stage of the parasite that enters water from the mouth of bird (heron) during the heron’s feeding in the water? Q2. What is the infective stage of the parasite to the (a) snail, (b) fish, (c) bird (heron)? Q3. What is the mode of transmission of the parasite to (a) snail, (b) fish, (c) bird, (d) human? Q4. What is the stage of the parasite found in the body of (a) snail, (b) fish, (c) bird? Q5. What do you think are the best control methods the parasite?

The best control of C. marginatum, and all other digenean trematodes, is to break the life cycle of the parasite. For instance, the parasite’s life cycle can be broken by elimination of the first intermediate host, the snail especially in aquaculture systems. In this regard, addition of copper sulfate solution in ponds has been used with limited success and is most effective against snails when applied at night, due to their nocturnal feeding activity. Also refer to Table 9.2. B. Cestodes (Tapeworms) Unlike the fish flukes, cestodes are almost entirely endoparasites whose adults live in the digestive tract (GIT) of their hosts. Tapeworms are characterized by a long, flattened and segmented body which often tapers towards one end. A distinct head ( Scolex) is present which has several small suckers followed by long chain of segments ( Proglottides) as in Fig. 9.5.


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Suckers

Segments Scolex

Fig. 9.5. A fish tapeworm

The Scolex (head) consists of suckers or hooks for attachment to the host tissue; whereas the segments (proglottides) consist of reproductive structures including eggs. As the segments become sexually mature a portion of chain of segments (proglottides) is broken off the main chain and passes into the environment via fish excreta.

Activity:

Q1. Can you give some examples of cestodan fish parasites? Q2. What are the similarities and differences among these cestodan fish parasites?

Those cestodan parasites known to infect fishes are Proteocephalus ambloplitis

(commonly known as bass tapeworm), Ligula intestinalis (commonly known as ribbon tapeworm), Diphyllobothrium latum (commonly known as fish tape worm) and Bothriocephalus acheilognathi . Among these four common fish tape worms, the major characters of only P. amblopitis and D. latum are given in Table 9.3.


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Table 9.3. Some major characters of two representative fish tape worms

Character Mode of parasitism Attachment organ Life cycle Definitive host Interm. host Developmental stages Infective stage to def. host (fish) Infective stage to interm. Host (copepod) Infective stage to human Mode of transmission to def. host Mode of transmission to interm. host Mode of transmission to human Treatment of infected fish Prevention of human or zoonotic infection

P. ambiloplitus Endoparasites

D. latum Endoparasites

Hooks or suckers (see Fig. 9.5)

Procercoid larva

Hooks or suckers (see Fig. 9.5) Indirect ( 2 species of hosts are required):Fish & Copepod Copepod Copepod Egg, Coracidium larva, Procercoid larva, Plerocercoid larva and Adult Procercoid larva

Eggs

Coracidium larva

Plerocecoid larva

Plerocercoid larva

Ingestion of the parasite with intermediate host (copepod)

Ingestion of the parasite with intermediate host (copepod)

Ingestion of eggs in the water

Penetration of coracidium larva into the copepod body

Ingestion of plerocercoid in the fish muscle

Ingestion of plerocercoid in the fish muscle

Bathing in praziquantal praziquantal solution Serving well cooked fish

Bathing in praziquantal praziquantal solution Serving well cooked fish

Indirect ( 2 species of hosts are required): Fish & Copepod Fish Fish Egg, Procercoid larva, Plerocercoid larva and Adult

Dear student, in Table 9.3 we have compared the two representatives representatives of tape worms in terms of various characters most of which revolve around their life cycle. Let’s now briefly describe the life cycle of these parasites. The


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diagrammatic diagrammatic representation of P. ambloplitus (bass tape worm) is shown in Fig. 9.6. •

The adult stage lives in the intestine of the fish and thus eggs pass into the water with fish droppings.

•

The eggs are eaten by the intermediate host, copepods, in which they hatch into a larval stage, procercoid.

•

When copepod is eaten by fish the larval stage gets access in to the fish where it undergoes further development to become plerocercoid that ultimately becomes adult in the intestine of the host. The cycle repeats.

Fig. 9.6. Life cycle of Bass tapeworm, Proteocephalus ambloplitis

Activity:

Dear student, by comparing Table 9.3 with Fig. 9.6, what difference do you observe between the life cycle of P. ambloplitus (bass tape worm) and D. latum (fish tape worm)?


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In case of P. ambloplitus (bass tape worm) eggs of the parasite shed into the water are directly ingested by the intermediate host (copepods). However, in case of D. latum (fish tape worm) the eggs passed into water via the fish droppings hatch into a larval stage known as coracidium that will subsequently penetra penetrate te into the body of copepods.

ctivity:

Dear student, I hope that you have got a picture of the life cycle, developmental

stages

and

modes

of

transmissions

of

the

representative representative fish tape worms from our ou r discussion so far. From your knowledge of the topic, Q. what do you think could be the public and socio-economic impacts of thes these e fish fish ta e worm worms? s?

The plerocercoid larvae are the most damaging parasites to freshwater fish. They decrease carcass value if present in muscle, and impair reproduction when they infect gonadal tissue. Problems also occur when they damage vital organs such as the brain, eye or heart and symptoms of tapeworm infections may be a swollen abdomen, swimming difficulty and wasting or killing. Therefore, economic impact from fish death can be significant in aquaculture systems. There is also a possibility of zoonotic infection when the plerocercoid exists in fish muscle. However, it is possible to avoid the infection by avoiding uncooked or undercooked fish. Activity:

Dear student, from the description of the life cycle of D. latum using only words and arrows sketch the life cycle of D. latum.


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9.2.2.2. Nematode Parasites of Fishes These are commonly known as roundworms and have elongated nonsegmented body tapered at both ends lacking suckers as shown in Fig. 9.7. Examples include Camalanus, Capillaria, Contracaecum and Eustrongyloides. The developmental stages of nematodes comprise egg, four larval stages and adults. These are endoparasites with a dult roundworms living in fish intestine whereas the larval stages are found in almost the entire internal organs and muscle tissue.

ctivity:

Q1. Do you think that the fish nematodes have direct or indirect life cycle? Q2. How do you think that these fish parasites can be prevented or treated?

The fish nematodes have complex indirect life cycles involving various hosts including copepods, insect nymph, birds, mammals; and fish can serve as both intermediate and final hosts. Nematodes can cause problems to fish. In severe infections, they may be seen protruding from the vent. Zoonotic infections are possible if raw or poorly cooked fish is consumed. The parasites can be prevented by breaking the life cycle and infected fishes can be treated using appropriate antihelmintic drugs such as fenbendazole.


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Fig. 9.7. A fish roundworm

9.2.2.3. Annelid Parasites of Fishes

These are commonly known as true or ringed worms. Annelid parasites of fish include leeches that serve as vector to transmit blood parasites including Trypanosoma and Trypanoplasma. Leeches could attach to the host internally in the throat region or externally to a skin as shown in Fig. 9.8.

Fig. 9.8. Leeches externally attached to fish body


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9.2.2.4. Acanthocephalan Parasites of Fishes

Acanthocephalan parasites are commonly known as spiny or thorny headed worms due to their possession of spines like structures as in Fig. 9. 9.

Proboscis with spiny structures

Fig. 9.9. Acanthocephalan Acanthocephalan fish parasite

They are internal or endoparasites highly specialized for life in the digestive tract of their fish host. They have indirect life cycle with crustaceans serving as the intermediate intermediate host. Acanthocephalans Acanthocephalans rarely cause problems in captive or aquaculture fish.

9.2.3. Copepod Parasites of Fishes These are crustacean arthropods that are parasitic to fish. Copepod parasites of fish are basically ectoparasites that exist on the external body surface of fish. Examples include Argulus (commonly called fish louse) and Ergasilus (commonly called gill maggot or gill louse). Fig. 9.10 demonstrates some structural features of fish louse and gill maggot.


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(a)

(b)

Fig. 9.10. Crustacean fish parasites (a) Argulus (fish louse), (b) Ergasilus (gill maggot)

Activity:

Dear student, Q1. What do you think are the effects of fish lice and gill maggots to fish? Q2.What are the possible treatments of fishes infested by these ectoparasites? Argulus (fish lice) attach themselves to the skin and fins and feeds on blood

of their fish host. Consequently, •

They may cause intense irritation to the fish that will in turn cause the fish to scratch against rocks

•

Heavily infested fish may be seen jumping out of the water because of the irritation.

•

Red lesions occur where the lice have attached, and this opens the skin up to secondary bacterial and fungal infections.

Ergasilus ( Gill Gill maggots or lice ) are usually found attached to the gills, gill

covers and inside the mouth. Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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•

Heavy infestation by gill maggot can result in severe gill damage, emaciation, anemia and death.

Both Argulus and Ergasilus parasites, because they suck blood, can transmit certain infections between fish. Treatment of these ectoparasites requires use of an organophosphate insecticide and baths of infested fishes Trichlorfon.

Activity:

Dear student, with our discussion so far we are coming to a conclusion on some of the major parasites of fish. Q1. As part of our conclusion, from your knowledge on fish diversity, can you give examples of fishes that are parasitic to other fish?

9.3. Major Fish Diseases The known major fish diseases are infectious being caused by the pathogenic parasites such as bacteria, viruses and fungi. Many of the fish diseases have no known therapy (cure), and thus prophylaxis (prevention) is the only control measure. As we have already discussed in our introduction to the chapter, fish diseases are more common and cause major problems in fish farming or aquaculture settings than in natural environments. Dear student, in sections 9.3.1 through 9.3.3 we will briefly discuss about the fish diseases caused by bacteria, viruses and fungi.

9.3.1. Bacterial Diseases of Fishes

Some of the major bacterial fish diseases are summarized in Table 9.4.


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Table 9.4. Some of the major bacterial fish diseases.

Disease

Causative agent

Effect

Fish infected

Furunculosis

Gram negative

Development of

Mainly

bacteria (Aeromonas

furuncles (small

Salmonids

salmonicida)

swellings) on skin

Columnaris

Flavobacterium

Gill & cutaneous

Mainly eels,

(saddleback disease)

columnare

infection

salmonids, cyprinids, etc

Enteric red mouth

Gram negative rod

Reddening of the

Mainly

disease ( Yersiniosis) Yersiniosis)

bacteria (Yersinia

throat and mouth

Salmonids

ruckeri)

and haemorrhages along the gumline of the mouth and the tongue

Edwardsiellosis Edwardsiellosis

Gram negative

Muscle lesion

Cyprinids

bacteria (Edwardsiella

and others

tarda)

Vibrosis

Gram negative

Primarily skin lesion

bacteria (Vibrio) Pasteurellosis

fishes

Photobacterium

Spleen and kidney

damselae

infection

Rainbow trout fry

Flavobacterium

Acute septicemia

syndrome (Bacterial

psychrophilum

with spleen

cold water disease ) Marine flexibacteriosis

Variety of

Salmonids

hypertrophy Flexibacter maritimus

Eroded and

Marine fish

hemorrhagic mouth, ulcerative skin lesions, frayed fins, and tail rot.


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Pseudomonaiasis Pseudomonaiasis (red

Pseudomonas species

spot disease)

Septicemia with abdominal distention and hemorrhage of skin and internal organs

Streptococcosis

Cocci bacteria such as

Central nervous

Lactococcus garvieae

damage involving exophthalmia ("popeye") and meningoencephalitis

Bacterial kidney

Gram-positive

disease

bacteria

Kidney infection

Salmonids

Many fishes

(Renibacterium salmoninarum)

Mycobacteriosis (fish

Mycobacterium

Tuberculosis

tuberculosis)

species

development

Piscirickettsiosis

Piscirickettsia salmonis

Dear student, let’s know have a brief look at a few of the fish bacterial diseases summarized in Table 9. 4.

A. Furunculosis

Furunculosis is a bacterial disease that results in the development of blisters or small swellings known as furuncles on the skin of the infected fish. This is a bacterial disease caused by a gram negative Aeromonas salmonicida sub sp. Salmonicida.


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Activity:

Dear student, do you think that the development of furuncles on the skin of infected fishes is a confirmation of infection by Aeromonas salmonicida sub sp. Salmonicida?

The formation of furuncles cannot be a sure sign of the disease because furuncles could also occur in other types of infections plus in acute cases of Furunculosis, furuncles may not be formed.

Activity:

Dear student, which fish groups do you think are mainly affected by this disease? Furunculosis causes economically devastating losses in cultivated salmonids in fresh and marine waters. It also affects a variety of non-salmonid fish and shows a widespread widespread distribution.

B. Vibriosis

Virbriosis is a bacterial disease caused by various species of a genus Vibrio, which is a Gram-negative bacterium possessing a curved rod-shape. Vibrio usually enters fish through the surface wounds and acts mostly on the skin, where lesions are formed. The ulcers can extend deep in to the muscles and internal haemorrhage, kidney damage and a swollen spleen are sometimes found in dying fish. It infects a great variety of warm and cold water fish species of economic importance. The disease is known to be accelerated at higher temperature.


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C. Mycobacteriosis

Mycobacteriosis is also known as fish tuberculosis, piscine tuberculosis, acidfast disease, granuloma disease, etc. It is a wasting disease known to affect near 200 freshwater and saltwater species.

It is caused by a large number of Mycobacterium species such as M. marinum M. fortuitum, M. chelonae, M. smegmatis, M. abscessus , M. neonarum, M. simiae, M. scrofulaceum and M. poriferae Activity:

Dear student, what do you think are the effects of the disease Mycobacteriosis to the infected fishes?

Fish infected with tuberculosis may become lethargic, hollow bellied, pale, show skin ulcers and frayed fins, have fin and scale loss, and loss of appetite. Yellowish or darker nodules may appear on the eyes or body and may deform the fish.

9.3.2. Viral Diseases of Fishes

Activity:

Dear student, we now proceed to the discussion of some of the fish diseases caused by viruses. Can you mention some of the viral fish diseases?

Some of the fish diseases caused by viruses include infectious pancreatic necrosis (IPN), infectious haemtopoietic necrosis (IHN), Infectious dropsy of carp (IDC), viral haemorrhagic septicaemia (VHS), channel catfish virus disease (CCVD), carp pox (CP) and lymphocystis . We will briefly discuss only a few of these viral fish diseases below. Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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A. Infectious Pancreatic Necrosis (IPN)

Activity:

Dear student, can you mention the effects and symptoms of fishes affected by this disease? This viral disease causes necrosis in pancreatic tissue and is also characterized characterized by the occurrence of clear clear or milky mucus in the intestine. intestine. At extreme situations the infected fishes undergo a characteristic “whirling behaviour” in which the fishes swim in a rotating manner about their axis, and death occurs in an hour or so.

Prior to this stage, however, the affected fishes may remain on the bottom, showing weak respiration and conclusive movements. It is common in salmonids and is transmitted from fish to fish and from parent to progeny through seminal fluids or infected eggs.

Activity:

Dear student, how do you think that this viral disease can be treated or prevented especially in farmed or aquaculture systems?

Since there is no effective treatment for IPN, the only means to control the disease is through preventive measures, which include the incubation of virus free eggs and propagation of IPN-free fishes in uncontaminated water in aquaculture systems.


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B. Viral haemorrhagic septicaemia (VHS)

This is an acute to chronic viral disease characterized by the clinical signs of dark appearance of fish, lethargic fish, and haemorrhages in the fin sockets. With the advance of the disease, the fish becomes nearly black and develops acute anemia. The gills become pale in colour and bleeding occurs in the gills and muscle. Prevention is more important as in the case of other viral infections there is no known cure for VHS.

C. Lymphocystis

This is a viral disease that occurs in several species of freshwater, brackish water and marine species of fish. It occurs as abnormally large white lumps or nodules on the fins or other parts of the body. The disease is highly contagious and especially under culture conditions it can spread rapidly.

Like other viral diseases lymphocyctis has no known cure and prophylaxis (prevention) is the only means of control. In culture systems the infected fish should be destroyed to prevent the spread of virus and the rearing facilities should be thoroughly disinfected in aquaculture systems.

9.3. 3. Fungal (Mycotic) Diseases of Fishes

Dear student, lastly in fish disease we are going to discuss about the fungi caused diseases. Two of the common fungal or mycotic fish diseases are saprolegniasis and branchiomycosis. branchiomycosis.

A. Saprolegniasis

Saprolegniasis is a fish disease caused by a fungus of Saprolegnia species. The disease affects skin and gills of freshwater fish and crustaceans. It is also


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known that the disease is also caused by non-saprolegniaceous fungi such as Pythium and Leptomitus.

Activity:

Dear student, Q1. Can you mention any identification characteristics of fungi such as Saprolegnia in infected fishes? Q2. What does Saprolegnia infection cause to the fishes? Q3. How can the Saprolegnia infection be treated in aquaculture systems?

The causative agents can be identified by the characteristic profusely branched, non-separate, cotton-wool like tufts of mycelium. In Saprolegnia infection lesion may appear as grey white patches on the skin, fins, eyes, mouth and gill. The colour may change to dark grey or brown as the mycelium tangle tangle and trap debris. debris. Under culture culture systems some chemical treatments with potassium permanganate, common salt, copper sulphate and malachite green may help.

B. Branchiomycosis Branchiomycosis

This fungal disease that causes a gill rot and caused mainly by two species of Branchiomyces: B. sanguinis and B. demigrans. To prevent the infection dense

stocking should be avoided in culture systems, high concentrations of organic matter should be avoided and clean fresh water should be provided.


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References Allison, E. (1996). Stock assessment considerations considerations in lakes and reservoirs. In: Cowx, I. G. (ed), Stock Assessment In Inland Fisheries. Fishing News Books, Blackwell, Oxford. Beveridge, Beveridge, M. C. M. (1984). Cage and pen fish farming. Carrying capacity models and environmental impact. FAO Fish.Tech.Pap., (255): 131 p. Renyntjens, D ((1997). Handbook of Fisheries Officers, LFDP WP24, Ministry of Agriculture, Ethiopia. Fisheries Resources Development Plan Study (October, 2004). Grant Proposal by the Federal Democratic Republic of Ethiopia, Funded by the African Development Fund. Food and Agriculture Organization Organization of the United Nations (2002). The State of World Fisheries and Aquaculture. FAO Fisheries Department, Rome. Food and Agriculture Organization Organization of the United Nations (2004). The State of World Fisheries and Aquaculture. FAO Fisheries Department, Rome. Food and Agriculture Organization Organization of the United Nations (2006). The State of World Fisheries and Aquaculture. FAO Fisheries Department, Rome. Food and Agriculture Organization Organization of the United Nations (2008). The State of World Fisheries and Aquaculture. FAO Fisheries Department, Rome. Food and Agriculture Organization Organization of the United Nations (2010). The State of World Fisheries and Aquaculture. FAO Fisheries Department, Rome. Gulland, J.A. & Rosenberg, Rosenberg, A.A. (1992). A review of length-based approaches to assessing fish stocks. FAO Fisheries Technical Paper 323. Guerrero, R.D. III, 1982. Development, prospects and problems of the tilapia cage culture industry in the Philippines. Aquaculture, 27:313–315. Holmer, M., Black, K., Duarte, C. M., Marba, N., Karakassis, I. (2008). Aquaculture in the Ecosystem. Springer Science and Business Media B.V. Karagiannagos, Karagiannagos, A. (1995). Fisheries Management in the European Union. Ashgate Publishing Limited, England. Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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King, M. (1995). Fisheries Biology, Assessment and Management. Fishing News Books, Blackwell, Oxford Ministry of Agriculture and Rural Development (April 2009). National Aquaculture Development Strategy of Ethiopia. Funded and supported by Food and Agriculture Organization Sub-Regional Office for East Africa. Noga, E. J. (2010). Fish Disease: Diagnosis and Treatment. 2 nd ed. WileyBlackwell, USA. Reyntjens, D. & Tesfaye Wudneh (1998). Fisheries Management_A review of the current status and research needs in Ethiopia. SINET: Ethiop.J.Sci. , 21 (2): 231-266.

Sidorkewicj, Sidorkewicj, N.S., Canzorla, A.C.L., Sabbatini, M.R., Fernandez, O.A., Domaniwaski, J.C.J. (1998). Interaction of common carp with aquatic weeds in Argentin drainage channels. Aquatic Management, 36:5-10. Welcomme, R. L. (2001). Inland Fisheries Fisheries Ecology and Management. Management. Blackwell Science, London.


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Recommended Additional Reading Materials

Allan, J.D. (1995). Stream Ecology. Chapman & Hall. London. Begon M., Colin R. T. and John L. H. (2006). Ecology: From Individuals to Ecosystems, 4th ed.,Blackwell ed.,Blackwell Publishing Ltd, Oxford. Cole, G.A. (1983). Textbook of Limnology. (3rd ed.) The C.V. Mosby Company, St. Louis. FAO Training Series No.21/1, 21/2 (1998). (1 998). Management for Freshwater Fish Culture and Farm Management. Fuiman, L. A. and Werner, R. G. (2002). Fishery Science: The Contribution of Early Life Stages. Blackwell Science Ltd, UK. Goldman, C.R. & Horne, A.J. (1983). Limnology. McGraw-Hill Book Company, New York. Horne, A.J. and Goldman, C.R. (1994). Limnology. MacGraw Hill, New York.

Moss, B. (1998). Ecology of Fresh Waters, Man and Medium. Blackwell Scientific Publications, London. Pillay, T. V. R. (1993). Aquaculture: Principles and Practices. Practices. Fishing News Books, UK. Scheffer, M. (1998). Ecology of Shallow Lakes. Chapman and Hall, London. Swift, D. R. (1993). Aquaculture Training Training Manual. Fishing News Books, UK. Wetzel, R. and Likens, G. (2001). Limnology. Academic Press.


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Appendix 1: Data on the status s tatus of world fisheries production by FAO (2000Table1), FAO (2008-Table 2) and FAO (2010-Table3). Table 1: FAO (2000) World fisheries production and utilization


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Table 2: FAO (2008) World fisheries production and utilization


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Table 3: FAO (2010) World fisheries production and utilization


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Appendix 2: Assignment Questions Instruction

The following questions will constitute not less than 25 % of your total marks. You should answer all the questions. You should be self dependent while working out all the questions. Copying from others or any form of plagiarism in relation to the answers for the questions will lead to disqualification of your total marks when discovered by the instructor in charge of the course.

1. Give some examples of fishes that are exceptions to: (a) Gill breathing (b) Possession of paired fns 2. What are the characteristics of fishes that make them diverse? List at least five examples 3. What is the basic difference between agnathan and gnathostoman fishes? 4. What kind of aquatic environments does each of the following fish groups inhabit? (a) Cyclostomes (b) Chondrichthyes (c) Osteichthyes 5. What are the various types of aquatic habitats occupied by various groups of fishes? 6. Define heterosexuality, bisexuality and unisexuality in fishes 7. What are the differences among the simultaneous hermaphroditism, sequential hermaphroditism hermaphroditism and serial hermaphroditism in fishes? 8. How is sperm transferred from male to female in fishes undergoing internal fertilization? 9. Distinguish between spawning and recruitment in fishes? Mulugeta Wakjira, Department of Biology, Jimma University, June 2011,

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10. List down the various developmental stages in fishes 11. What are the two major forms of fisheries? Define each. 12. Give four examples of fishing gears and methods, and show their similarities and differences. differences. 13. Give examples of commercially important fishes in the: (a) World (b) Ethiopia 14. What are the differences among pond culture, cage culture, pen culture and tank culture? 15. What are the differences among extensive culture, intensive culture and semi-intensive culture? 16. Distinguish among integrated culture and polyculture 17. What is the current status or trend of capture fisheries and aquaculture production in the world? 18. Discuss the past and present development history of Ethiopian capture fisheries 19. Discuss the nutritional content and values of fish diet 20. Discuss the socio-economic benefits of fisheries and the role of fisheries in improving food security security 21. List down the post-mortem changes in fish and relate each to fish quality. 22. List down and define each of the preliminary fish processing stages 23. List down the various fish preservation methods and how they work 24. What is a fish stock, and a fish stock assessment? 25. What are the various methods or strategies used to ensure sustainable exploitation of fisheries resources? 26. List down the various major groups of fish parasites and give some specific examples for each major group. 27. List down some examples of fish diseases caused by bacteria, virus and fungi with their species or genus level causative agents.


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Fisheries and Aquaculture

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