Guide to the small scale artificial propagation of trout · artificial reproduction of rainbow...

GUIDE TO THESMALL SCALE ARTIFICIALPROPAGATION OF TROUT

Authors: GYÖRGY HOITSY,ANDRÁS WOYNAROVICH and

THOMAS MOTH-POULSEN

Authors:GYÖRGY HOITSY,ANDRÁS WOYNAROVICH andTHOMAS MOTH-POULSEN

GUIDE TO THESMALL SCALE

ARTIFICIAL PROPAGATION OF TROUT

Budapest, 2012

Photos and illustrations by courtesy of

GYÖRGY HOITSY

The designations employed and the presentation of material inthis information product do not imply the expression of any opin-ion whatsoever on the part of the Food and Agriculture Organi-zation of the United Nations (FAO) concerning the legal ordevelopment status of any country, territory, city or area or of itsauthorities, or concerning the delimitation of its frontiers orboundaries. The mention of specific companies or products ofmanufacturers, whether or not these have been patented, doesnot imply that these have been endorsed or recommended byFAO in preference to others of a similar nature that are not men-tioned. The views expressed in this information product are thoseof the author(s) and do not necessarily reflect the views of FAO.

2

This book aims to provide basic information on reproduction andpropagation of trout, tries to describe most important hatcheryactivities and challenges and also provides advices on the rear-ing of trout fry in order to support small scale farmers and pro-ducers. As small scale fish farming is a substantial opportunity togenerate income and also provides a valuable protein source itis important to afford knowledge about the proper technology.

Authors wish to express their gratitude to Ms. ÉVA KOVÁCS,Junior Aquaculture Officer (FAO-REU) for her contributionto the English version of this document.

Thanks are also due to Mr. ISTVÁN FÁBIÁN (www.ajel.huand [email protected]) for the typographical design and workof this publication.

PREFACE

ACKNOWLEDGEMENT

3

Preface 3Acknowledgement 31 Introduction 52 Reproduction of trout in the nature 5

2.1 Reproduction strategy 52.1.1 Reproductive age and number of times

spawning occurs in a lifetime 52.1.2 Fecundity 62.1.3 Size of eggs 62.1.4 Reproductive behavior 6

2.2 Spawning 73 Reproduction of trout in fish farms 8

3.1 Preparation for propagation 83.2 Rearing and feeding of brood fish 103.3 Preparation of the hatchery 103.4 Works in the hatchery 11

3.4.1 Selection of suitable broodfish and stripping of eggs and milt 113.4.2 Incubation of eggs 143.4.3 Hatching and development of sack-fry 153.4.4 Rearing of fry 16

References 17Glossary 18

Table 1: Reproductive age and period of selected trout species 5Table 2: Size at sexual maturation, fecundity and duration of

eggs and sack-fry incubation of selected trout species 6Table 3: Key propagation data of brown and rainbow trout 13Table 4: Length of the incubation period of trout eggs under

different water temperatures 15Table 5: Dissolved oxygen content of fully saturated water

at different temperatures 19

Figure 1: Differences between females and malesduring reproductive season 9

Figure 2: Hand stripping of a female 12Figure 3: Stripping of milt onto eggs 12Figure 4: Fertilization (mixing of eggs with milt) 12Figure 5: Adding water to fertilized eggs 12Figure 6: Eyed eggs 12Figure 7: Hatched larvae 12Figure 8: Different incubation vessels for trout eggs and larvae 14Figure 9: Development of fertilised rainbow trout eggs

and hatched larvae at about 10 oC 16Figure 10: Typical fry rearing fibreglass tank 17Figure 11: Typical fry rearing tanks 17

Box 1: Development and ovulation of eggsin sexually matured bony fish 7

Box 2: Structure of trout egg and sperm 11

TABLEOF CONTENTS

Tables

Figures

Boxes

SMALL SCALE ARTIFICAL PROPAGATION OF TROUT4

1� INTRODUCTION

Small scale trout farming is a realistic in-come generating alternative in the moun-tainous regions of Central and EasternEurope, the Caucasus and Central Asiawhere income sources and employmentopportunities are scarce or even missing.

Though all female eyed eggs of wellperforming pedigree trout strains can bepurchased from many different locationsof the world propagation of locally main-tained trout can still be technically andeconomically feasible. Increased officialopposing of introducing fish strains withgenotypes new in a region is also an ad-ditional reason why practical knowledge ofartificial reproduction of rainbow trout maybe very useful.

It is expected that technical informationpresented in this book will help in the re-production of other trout species. It mayalso successfully complement recentlyproduced FAO publications such as Smallscale rainbow trout farming, Small scaletrout processing methods and Trout farm-ing based angling tourism.

In order to satisfy interests for furtherdetails a glossary is compiled and tablesand annexes are attached to this paper.For the sake of finding additional informa-tion asterisk symbols (*) are used afterwords in italics which are explained in theglossary.

Introduction / Reproduction of trout in the nature 5

2 � REPRODUCTIONOF TROUTIN THE NATURE

2.1 � REPRODUCTIONSTRATEGY

Not only growth but also the successfulreproduction of fish depends on the sur-rounding environment. For this reasondifferent species of fish develop andpractice different reproductive strategieswhich, in a characteristic way to species,ensure a successful offspring productioneven under fluctuating environmentalconditions.

Reproductive strategy of fish includesreproductive age, fecundity according tosize and age, size of eggs, reproductivebehavior and the number of times spawn-ing occurs in the lifetime of females (Bond,1996).

2.1.1 � Reproductive age andthe number of times spawningoccurs in a lifetime

In different fish species the length of time inwhich males and females become sexuallymature may vary between a few monthsand several years. The actual sexual mat-uration of trout depends on spe cies, sexand environmental conditions (water tem-perature, feeding conditions, etc.) in whichfish live and develop (see Table 1).

Table 1:Reproductive age

and periodof selected trout

species

Species

Rainbow trout

Brown trout

Brook trout

In nature

Sexual maturation(years)

Reproductive period(years)

Within farm conditions Within farm conditions

Females

3–4

3–4

3–4

Males

2–3

2–3

2–3

Females

2–3

3

2–3

Males

(1)–2

2

(1)–2

Females

4–6

4–6

2–3

Males

6–7

6–7

2–3

2.1.2 � Fecundity

Fecundity* of egg-laying bony fish speciesdepends on their parental care* and thesize of produced eggs. Fecundity of fish isex pressed with the absolute and relativenumber and the weight of eggs producedby a female. Table 2 summarises the fe-cundity of widely and frequently producedtrout species.

At trout reproductive behavior includestiming of spawning, selection and prepa-ration of spawning ground, courting andmating with selected males.

By mating season eggs and milt shouldbe ripe, ready for being fertilized (eggs) orto fertilize (milt). Spawning in the rightplace and time when both eggs and miltare ripe and all environmental conditionsare favourable is the final response of theendocrine* system of fish to environmen-tal cues.These are physical (temperature,clearness, speed and depth of water) andchemical (clean water, rich in oxygen)qualities of water, light, day-length, suit-ability of mating ground and presence ofthe opposite sex (Woynarovich and Hor-vath, 1980 and Bond, 1996). In otherwords favourable environmental condi-tions stimulate production, development,final maturation and ovulation of eggs(see Box 1).

Development and release of milt inmales is also influenced by environmentalconditions but nature built less endocrinecontrol into this process than into the onefor females.


Rainbow trout

Brown trout

Brook trout

Females(kg)

1–7

1–6

1–3

Males(kg)

1–4

1–4

1–1.5

Absolute (egg/fish)

1–10

0.5–8

0.5–5

Relative(egg/kg BW*)

1.6–3.0

1.6–3.6

1.2–2.5

Up to eyed-eggstage

1601

195–2731

195–2761

Total

3101

250–4061

235–4441

Swim-up

5001

380–6101

338–6751

Size ofbroodfish

Fecundity of female (1000 eggs)

Incubation of egg

Duration (Do)

Species

Table 2:Size at sexual maturation, fecundity and

duration of egg and sack-fry incubation ofselected trout species

Source:1. Bascinar andOkumus, 2004,

2.1.3 � Size of eggs

Egg sizes of fish indicate the size of yolk-sack in developing embryos and non-feeding larvae which are also calledsack-fry (see Figures 9).

Salmonid eggs are the largest amongthe eggs of bony fishes. The size of theirdry eggs varies between 3.7 and 5.2 mm(32–100 mg) (Hoitsy, 2002). Egg size ofyounger and smaller females may besmaller than that of the elder and largerones. Eggs of 5–6 year-old females arethe largest but the quality and quantity offeed also influences the actual size ofthem The volume of 1 000 eggs may be79–90 cm3.

The large size of trout eggs can be ex-plained with the long duration of egg andsack-fry incubation.

2.1.4 � Reproductive behavior

Reproductive behaviour is a complex se-quence of sexually mature female andmale fish which aims to ensure the high-est possible survival of laid and fertilisedeggs and hatched non-feeding larvae.

2.2 � SPAWNING

Most of the trout species are diadromous*,more precisely anadromous* fishes. Still,those riverine* and lacustrine* trout spe -cies which habituated fully to freshwaterenvironment, hence never move into theseas, also migrate for spawning to uppersections of rivers and their tributaries.

Shortening days and decreasing watertemperature affect hormone concentrationof brood fish. This causes rhe develop-ment of secondary and accessory sexcharacteristics, drives reproductive beha -viour and triggers reproductive activities.

Light conditions have a very importantrole in the reproductive behaviour and ac-tivity of trout. Shortening days stimulatedevelopment of eggs and activate in-stincts of spawning migration. On largebroodfish farms where the objective is acontinuous, year-round propagation andeyed-egg production light conditions arealso controlled in order to stimulate andsynchronize ovulation in females.

Changes of water temperature also pri-marily stimulate and synchronise ovula-tion in females. If it decreases autumnspawning strains, while if increases springspawning strains will prepare for spawn-ing. If season specific trend of water tem-perature changes (increase in autumnand decrease in spring) preparation forspawning will stop.

Dissolved oxygen (DO*) content ofwater is also a prime environmental con-dition which drives and influences thespawning of trout. Trout are mostly autumnspawning fishes since they are the mostDO demanding fish species therefore ahigh DO is needed for the proper devel-opment of their embryos and sack-larvae.This environmental condition will morelikely occur during winter as DO content ishigher in colder waters. Swim-up of fry isusually finished by the end of the winterwhich reduces possible losses that melt-ing snow and spring floods may cause.

Water current conditions, water depthand bottom types have less role in thefinal maturation and ovulation of eggs.

For the above described reasons troutspawn seasonally. Actual spawning sea-son depends on species and strainshence it might be either in autumn or in

spring. Spawning of trout takes place inthe headwaters and tributary streams ofrivers or in the inlet or outlet streams oflakes (Edwards, 1989).

Spawning of trout is wonderful whichcan be observed in cold mountain riversand larger streams where they leave. Fe-males and males swim up to the uppersections of rivers and streams and theyeasily pass rapids as high as 0.5–1 meter.They swim in the dark during evening and

Reproduction of trout in the nature 7

Development and ovulation* of eggsin sexually matured bony fish

By about the first months after swim-up and starting exter-nal feeding of young fish fibre-like initials of the gonads*(ovary* and testis*) are already formed. In this stage the ovary already contains the primitive eggcells (oogonium, ovogonium or archovogonium) from whichthe eggs will develop when the fish reaches sexual matura-tion. Evidence of sexual maturation is when a first produc-tion cycle of eggs suitable for ovulation and fertilization*occurs. Development of egg batches in the ovary beforeeach spawning is a precondition of successful reproduction.This process has different subsequence phases:1. A batch of primitive egg cells (oogonia) in the ovary

transforms into primary oocytes*.2. A follicle* is formed around each primary oocytes.3. Eggs undergo a quantitative development called vitello-

genesis* when yolk builds into the eggs in four subse-quent steps. This phase is a longer procedure which iscompleted before the spawning season. During vitello-genesis a properly balanced feeding of females is es-sential.

4. Though eggs are ready for final maturation and ovula-tion when the vitellogenesis is completed still there is adormant (resting) stage* in their development. The rea-son for it is that the future of fertilized eggs depends onthe timing of spawning when environmental conditionsare most suitable for laid and fertilized eggs.

5. Dormant phase of eggs in the ovary ends when environ-mental conditions become favourable for spawning. Atthis time favourable environmental stimuli arrive into thebrain of fish through sense organs. A complex neuro-en-docrine process* starts in the brain which results in theovulation of eggs and spawning of fish.

Depending on fish species the above described proceduremay be continuous within a well defined shorter or longerperiod of the year or it can be seasonal as it is in case oftrout.

After: Woynarovich and Horváth, 1980

Box 1

night time in order to reach their spawn-ing ground by dawn.

At the spawning ground femaleschoose the most suitable location wherethe bottom is covered with pebbles andthe water is swift. Here they make theirshallow nests (also called redd) by clean-ing an area of about 0.5–1 meter diame-ter. These hollows on the bottom ofstreams and rivers indicate the presenceof an active trout population. When nestsare ready their bright clean pebbles willcontrast with surrounding bottom coveredwith greenish or brownish algae.

Males follow females. This time theyare aggressive and fight for females. Thestrongest male occupies the nest with thefemale where they mate in the early hoursof the day.

At mating the female stops in the frontwhile the male stands behind her. Thenthe female bends in a “C” shape andpresses the ovulated eggs out with a peri-staltic* movement of her muscles. Whenthe female positions herself and is pre-pared to release the eggs the male joins.He also bands in a “C” shape close to theside of the female and fertilizes the re-leased eggs. They have to be fast and ac-curate because only a very short period oftime (sometimes even seconds) is avail-able to fertilize the released eggs whichare quickly drifted away by currents.

One spawning nest may be used bymore than one couple. Trout do not guardtheir nests but males may remain aroundand chase away intruding fishes. Laterthey also leave the site.

Some publications of trout spawningdescribe trout as a fish which covers itseggs with fine pebbles or even by sand.This is incorrect because trout has themost oxygen-demanding eggs thereforeany action to cover and hence cut them offfrom open, oxygen rich water currents israther unlikely.

3. � REPRODUCTIONOF TROUTIN FISH FARMSTrout becomes sexually mature in fishfarms sometimes even earlier than in na-ture if water temperature is higher andfeeding is better than there.

As many other fish species, trout alsocan reach sexual maturation in fish farms.Females and males will produce eggs andmilt (gametes*) but they can not spawnsuccessfully under regular fish farm con-ditions unless all required favourable en-vironmental conditions are simulated.Though, reliable production of large quan-tities of fertile eggs and hatched larvaewould be both difficult and expensive onthis way. Therefore, there are other moreefficient ways of artificial propagation* oftrout which result in the ovulation of eggsstripped and fertilized with milt frommales.

3.1 � PREPARATION FORPROPAGATION

On a fish farm the sign of the arrivingpropagation season is that sexually ma-tured females and males gather at the in-flow of their tank near to the water surfaceand often try to jump against the watercurrent. This indicates that females andmales are ready to migrate to spawninggrounds. At this time females and malesshould be separated. Otherwise alreadyripened brood fish will spontaneouslyspawn while others will pick and consumereleased and fertilised eggs from the bot-tom of the tank where this uncontrolledspawning takes place.

In trout sexes can easily be distin-guished during the propagation season(see Figure 1). Therefore separation of fe-males and males can be safely com-pleted:

Males are slimmer and their back ishigher and humpy. Their colours arebrighter. Their lower jaw is pointed andwedge shaped. At elder age lower jawtakes a hook shape and is covered with


swollen growths. Their pointed urogenitalpapilla sticks out from which white milk-type sperm bursts if the abdomen is gen-tly pressed.

Females are more round and filled atthe belly because of their enlarged ovary.Their urogenital papilla sticks out about 1–2 cm and is top is rounded (see Figure 1).

Fishing and sorting of brood fishshould be done gently with care in ordernot to stress and hurt the fish which arefull of eggs and milt.

On large tout farms which are special-ized on propagation, ovulation and sper-miation are induced with hormones such assalmon hypophysis* or Gonadotropin Re -leasing Hormone Analogues (GnRH/A*).However, most of small scale trout farmsdo not use hormones to harmonise andcomplete ovulation in females and sper-miation in males. These fish farms imitatefavourable environmental conditions which

stimulate both final maturation and ovula-tion of eggs in females. If a fish farm issuccessful in the simulation of most im-portant favourable environmental condi-tions then less fishing and handling effortswill result in a higher quantity and betterquality egg production. This will also savebrood fish from unnecessary stresseswhen their readiness is checked.

The best way for simulation of favour -able environmental conditions is whenwater level is lowered and speed of wateris increased in freshly cleaned tankswhere females and males are separated. Ifit is done properly, about 50–70 percent offemales will be ready for stripping 7–10days after their separation. In case of au-tumn spawning females a slight reduction,in case of spring spawning females a slightincrease of water temperature is also aneffective way to imitate environmental con-ditions which will advance ovulation.

Reproduction of trout in fish farms 9

Those females which do not react onthe described manipulation of keepingconditions will perform a lengthy propaga-tion period when a successful strippingwill remain less predictable.

Figure 1:Differences between

females and malesduring reproductive

season

3.2 � REARING ANDFEEDING OF BROOD FISH

If eggs, fry or young fish are not pur-chased but are produced on a fish farmthe entire success depends on the qualityof brood stock which is kept and propa-gated there. Only those healthy femalesand males should be propagated whichhave a proven good life time performanceand are able to inherit them. Most advan-tageous traits are size, utilization of feeds,growth rate and overall resistance tostress and diseases.

It is a general rule for a positive selec-tion of brood fish that good genotypes*should be searched among fish with goodphenotypes*. It means that when a fish isselected for propagation its appearance,physiological properties and individualperformance should be considered.

It is advantageous to select futurebrood fish from a stock which is about 10month old. The most properly looking,largest and healthiest specimens from thesame age group should be selected for fu-ture propagations. From this time on se-lected and separated stocks of futurebrood fish should receive a different, lessprotein rich diet. If fish receive high proteindiet their muscles and body will grow in-stead of their gonads.Today well balancedfeeds are widely available for this purposewhere all the proteins, energy, vitaminsand minerals are contained in the rightquantity and proportion needed for grow-ing and grown-up brood fish. Sometimesalso other ingredients are added in orderto change the colour of the fertilized eggs*.

Under farm conditions male trout be-come sexually mature in the second year,while females in the thirds year with theexception of brook trout. About 60–70 per-cent of brook trout females become sexu-ally mature already by the second year. Innature both males and females need 1–2more years to reach sexual maturity.About 6–7 brood fish should be stockedper 1 m2 of tank area.

There are no specific criterions of agood brood stock rearing or keeping tank.It should be suitable for being cleaned andkept cleaned easily to avoid accumulationof faeces and unconsumed feeds. It should

also be suitable to change water in it about2–10 times per day.

On many fish farms males and femalesare kept separately during the entire year.Such practice has no considerable ad-vantages if basic reproduction relatedphysiological and ethological aspects arein focus. It is true that males and femalesshould be separated before the propaga-tion season. Still, some young malesplaced in the tank of females before prop-agation will help advancing and synchro-nizing ovulation in females. Even after themost proper stripping* of a female a littleportion of ovulated eggs will remain in thefish. If females cannot release these eggsand they remain in the fish they will nega-tively influence egg production next yearand eggs remained in the female maydecay and even cause mortalities. There-fore, if these females are kept togetherwith males they will drive out even the lastdrops of eggs from them. Males are veryaggressive during the propagation sea-son. If females are mixed with males afterstripping, aggressiveness of males will re-duce. Therefore, losses due to fightingand wounds will reduce too.

3.3 � PREPARATIONOF THE HATCHERY

Parallel to separation and preparation ofbrood fish for propagation fish hatcheriesshould also be prepared. It means:� Checking, repairing and cleaning of

both water supply and drainage sys-tems.

� Cleaning of brood fish tanks, trolleys,hatchery devices and equipment.

� Making ready weighing and measuringdevices.

� Completing and cleaning strippingbowls and towels.

Disinfection of the water supply anddrainage systems and hatchery devicescan be done with formalin.


3.4 � WORKSIN THE HATCHERY

Works in the hatchery include the choos-ing of suitable broodfish, stripping, fertil-ization and incubation of eggs and rearingof hatched fry.

3.4.1 � Selection of suitablebroodfish and stripping of eggsand milt

There are different techniques for remov-ing ovulated eggs and milt from broodfish.Elaboration of the first technique of artifi-cial propagation of trout copied naturalspawning. It was done by a German fishfarmer, Jacobi between 1763 and 1765.He stripped eggs into a jar of water. Todaynobody follows this “wet” technique be-cause the expectable rate of fertilization isas low as 20 percent.

In 1856 Vranszkij Russian fish culturiststarted a “dry” technique. Since this time thismethod has been successfully practiced be-cause it ensures 98–100 percent fertiliza-tion. The essence of this technique is thatfirst eggs then milt are stripped into a drybowl where they are gently mixed before fer-tilization starts with the adding of water.

The first step is the separation of thosefemales which already ovulated. Signs ofovulation are an enlarged and softened ab-domen. Eggs in the female can be felt whengently touching and the urogenital openingsticks out about 1-2 cm (see Figure 1).

There are different techniques for strip-ping ovulated eggs. According to the Aus-tralian one air is pumped into fish with asyringe and this is what presses eggs outof the female. The Swedish techniqueuses a double walled rubber pipe. Femaleis placed into this tube then water is in-jected between the walls of the tube. Theinner soft wall covers the entire bodywhich gently presses out the ovulatedeggs from the female.

A most widely practiced technique ishand stripping. This technique is simple.Head and tail of fish are wrapped intohandtowels and the female is firmly butgently hold at her two “ends” on a way thathead is 45 degree upward. This position

of fish allows driving the ovulated eggswith a gentle massage with the thumb andforefinger toward the urogenital openingfrom where eggs will directly pour into thestripping bowl.

In case of rough handling and unpro-fessional stripping fish may be hurt oreven injured. Therefore, instead of strip-ping everywhere from head to tail it shouldbe restricted only to the lower section ofthe belly. The stripping hand should notstart higher than an imaginary line be-tween the dorsal and the pelvic fins. If fishis stripped above the mentioned imagi-nary line its internal organs such asspleen or liver may be damaged whichcan result in mortality. Another reason whyfemales should be stripped at the lowersection of their bellies is that the ovulationof eggs starts in the lower section of theovary. Hence, there is no reason for strip-ping fish along the entire body.

Milt of males is stripped similarly toeggs. Gentle handling and stripping isvery important here, too.


Structure of trout egg and sperm

Egg: It has an animal pole* and a vegetal pole*. Egg shell ofbrown trout is about 33–37 microns thick while this is thin-ner at rainbow trout. On the egg shell about 1 micron porescan be observed which continue in narrow ducts. Microphylethrough which sperm enters is situated on the animal poleof the egg. After the first sperm enters it closes but withoutthe entering of any sperm the microphyle will also closewithin about a minute when the egg starts swelling. Periv-itelline space separates shell from the cell which fills withfluid within 20–60 minutes after fertilization. This fluid filledspace allows the embryo to rotate (gyrate) freely in the eggshell and to remain always in the right position. Duringswelling the volume of egg increases with about 12–20 per-cent. Trout egg is not adhesive but may stick to a substrateor to the wall of the hatchery devices until fully swelled.

Getting into the egg the germinal disk*, the vitelline mem-brane and yolk can be found. The yolk is a dense yellowishliquid which contains globulin* and oil droplets. These oildroplets accumulate in the upper animal pole of the egg inorder to keep the germinal disk at the right place and in thecorrect position.

Sperm: Head of the sperm is 1.7 by 2 microns and its tailis about 25–35 microns long. Active life of sperm starts whenejaculated into water and lasts for about 24–40 and 40–50seconds at brown trout and rainbow trout, respectively.

Box 2

Quick and gentle stripping of eggs isessential. Where larger quantities of fe-males are stripped MS 222 tranquilliser isused. Recently alternative, less expensivematerials are researched and used,among others clove oil.

Not only brood fish but also strippedeggs should be handled with care. If theyfall from a higher distance into the strip-

ping bowl or they are steered and mixedwith milt roughly they may loose their fer-tility and eggs will die.

Trout ovulate in batches with intervals.About 2-5 days after the first major ovula-tion when about 75-85 percent of the eggscan be stripped a smaller second ovulationoccurs. For this reason it is important eitherto check the already stripped females and


Figure 2: Hand stripping of a female Figure 3: Stripping of milt onto eggs

Figure 4: Fertilization (mixing of eggs with milt) Figure 5: Adding water to fertilized eggs

Figure 6: Eyed eggs Figure 7: Hatched larvae

strip them again or to place them togetherwith males. They will drive out later ovu-lated eggs from the females. Otherwiseovulated but not stripped or released eggswill decay in the fish. Even if this processwould not necessarily cause mortality, stillit will negatively influence the quality andquantity of egg production in the next year.

About 4-6 year old and 2.5-3.5 kg largefemales will produce the largest quantityand best quality eggs. Egg production ofelder than 6-year-old females will gradu-ally reduce both quantitatively and quali-tatively because of the accumulated effectof different stresses experienced by fish.

It is very important to avoid the contactof eggs with water before fertilization.

Therefore, before stripping fish - espe-cially their urogenital opening - should bedried with a towel.

One portion of stripped eggs, about 5000-10 000 pieces should be fertilisedwith the milt of at least 2 or 3 males. Thiswill ensure proper fertilization of all eggseven if, for some reasons, one of themales is unfertile. Males can be strippedagain after about 3-7 days. Therefore miltof good males can be used for the fertil-ization of eggs from many different fe-males. 1 male is enough to fertilize theeggs of about 3-8 females.

After stripping, eggs and milt shouldbe gently mixed still without water. If alleggs are covered with the film of milt they


Sexual maturation of females (years):

Sexual maturation of males (years):

Proportion of sexes:

Propagation season:

Eggs per 1 kg BW (No.):

Eggs in 1 kg of dry eggs (No.):

Quantity of milt per male (cm3):

Quantity of sperm in 1 cm3 milt:

Fertility rate of eggs (%):

Rate of hatching from fertilized eggs (%):

Length of embryogenesis at 10 °C (days):

Duration until eyed-egg stage at 10 °C (days):

Duration of sack-fry (none-feeding larvae) stage (days):

November–January

1 600–3 580

12 500–16 500

16 000 000

95–100

90–100

40–42

20–21

20–28

November–March(depending on the strain)

1 600–3 100

10 000–18 200

20 000 000

85–100

75–95

30–34

18–21

20–21

5–27

3

2

3–8 ♀:1 ♂

Brown trout

(Salmo trutta m. fario)Rainbow trout

(Oncorhynchus mykiss)

Table 3:Key propagationdata of brown andrainbow trout

should be left for about 1-2 minutes inorder to let them be fertilized. When eggsare fertilized a little fresh water should beadded then eggs should be gentlywashed clean with adding more freshwater to them. During this procedure bad,unfertile (white) eggs should be removed.They are white because proteins coagu-late in the unfertile eggs. After washingand cleaning eggs should be placed intohatchery devices.

3.4.2 � Incubation of eggs

During the last centuries many dozens ofdifferent types of incubation vessels wereinvented, developed and used.They weredifferent both in materials (ceramic, glass,wood, metal or plastic) and shape. TodayCalifornian, Sandfort and vertical tray in-cubators are used most widely (see Fig-ure 8) but cylindrical Zuger jars can alsobe found in many trout hatcheries.

When eggs are placed into incubationvessels - about 10 000 eggs/0.2 m2 - theyare less sensitive and bad ones should bepicked out for until about an additional 36

hours. Then the first sensitive period startsand lasts until eyed-egg stage. During thisperiod multiplying cells in the eggs arevery fragile. A bigger bump on the eggmay cause a malformation in the develop-ing embryo or even mortality. Thereforedeveloping eggs should be kept undis-turbed in hatchery devices. After eyed-eggstage until hatching eggs can be trans-ported, hand or machine sorted again andbad, damaged eggs can also be pickedout. It is because eggs are hardy duringthis period. Then from about 48 hours be-fore hatching they become fragile again.

During the first fragile period of eggsthe only prevention against saprolegnia*is the use of formalin in a concentration ofabout 0.25 ml/l. The use of specific iodinecontaining products is also feasibleagainst saprolegnia.

Since saprolegnia develops on deadand decaying eggs from which it canspread to healthy ones it is very importantto remove damaged and dead eggs assoon as they can be touched, regardlessif they are infected with saprolegnia or not.

There are contradicting opinions andpublications about light sensitivity of trouteggs. It is sure that most of trout eggs ex-posed to direct sunlight for a few minuteswill die. Therefore diffused light or evendarkness in the hatchery is widely recom-mended.


Figure 8:Different incubationvessels for trouteggs and larvae1. Californian hatchery,2. Sandfort hatcherytray and3. Vertical trayincubator

3.4.3 � Hatching anddevelopment of sack-fry

The actual time of hatching depends onwater temperature but oxygen content ofwater also greatly influences it. Hatchingbelow 4 oC and above 15–18 oC can onlybe done with great losses.

Eggs of rainbow trout and brown troutwill hatch within about 520 and 320 day-degrees* (Do). If in nature water tempera-ture is less than 2 oC, the development ofembryos stops. This diapause* causesgreat losses. It is especially important be-cause in nature, even if all environmentalconditions are optimal not more than 15–20 percent of eggs will hatch and only0.5–1 percent of fertilized eggs will surviveand grow to sexually mature adults.

After fertilization, at the start of cell-divi-sion, at pigmentation of the eyes and beforehatching oxygen demand of de ve lopingembryos will especially increase. Duringthese periods insufficient quantity of oxygenwill result in higher mortality or at the end ofthe embryonic stage as a result of oxygendeficiency earlier hatching will occur.

Before hatching embryos graduallymove (gyrate) more and more intensively.This movement mechanically thins the eggshell from inside. In addition, hatching lar-vae decompose the egg shell with an en-zyme (hyaluronidase) which is secreted bya gland found in the head of the embryo.

Eggs stripped from different femalesbut fertilized at the same time may hatchdifferently. This difference may be 2–3days. Hatching larvae tear open the eggshell with their tail and literally reversefrom it. Larvae which tear up the egg shellwith their head often die because the eggshell remains stuck on their head and gills,therefore they die of suffocation.

Larvae are hatched with a large yolk-sack from which they feed until switchingto external feeding. Yolk-sack might makeup for 2/3–3/4 of the entire weight ofhatched larvae.

Hatched larvae remain laying on thebottom of hatchery devices. Under nor-mal conditions they evenly occupy these.During incubation of non-feeding larvaeegg shells, dead larvae, floating greaseand oil drops should be removed fromwater surface. Developing non-feedinglarvae does not need any other care forabout 2–4 weeks (see exact duration inFigure 9). During this period only deadlarvae should be removed regularly fromthe devices.

It is important not to expose develop-ing larvae to strong light since then theywill try to hide under each other whichmay cause oxygen shortage, hence mor-tality. It is also important to keep the rear-ing devices clean. This is done by anappropriate exchange of fresh water andsiphoning of dead and decaying larvae.During this period larvae are sensitive tochemicals including formalin, therefore aclean rearing environment is the only op-tion for prevention.

As larvae advance in developmenttheir yolk-sack is gradually consumed andthey start to feed externally. They alsostart to move until finally they swim up tothe water surface and gulp air from the at-mosphere. External feeding starts still be-fore the yolk-sack is entirely consumed.This few days overlapping of internal(yolk-sack) and external feeding of larvaeensures a safe supply of nutriment forswim-up fry until they learn how to feed.By the time the yolk-sack is fully con-sumed fry learn how to feed from their en-vironment.


Table 4:Length of the

incubation period oftrout eggs under

different watertemperatures

Watertemperature (oC)

6

8

10

12

Days

77

61

41

27

Do

462

488

410

324

Days

55

43

31

26

Do

330

344

310

312

Days

80

62

40

38

Do

480

496

400

456

Brown trout Rainbow trout Brook trout

3.4.4 � Rearing of fry

After the swimming-up of fry their feedingshould start with properly balanced dryfeeds which contain the needed quality andquantity of proteins (50–60 percent), vita-mins and minerals. Size of the applied feedis also very important. It should only be aslarge as the developing fry can easily graband swallow. During the rearing of fry or asoften called advanced fry, intervals betweenfeedings should be about ½ hours. A sign ofinsufficient feeding is the increasing differ-ence between individual sizes of developingfry. This may result in serious cannibalism.

Tanks of different shapes are used forrearing fry. Few meters long troughs, rec-tangular or round tanks are the mostwidely applied rearing devices. At the be-ginning depth of water may vary between0.1 and 0.2 meters which should gradu-ally be increased to 0.5–0.8 meters.


Figure 9:Figure 9: Development of fertilised rainbow trout eggsand hatched larvae at about 10 oC1. Moment of fertilization,2. Early stage of blastula (7.5 hours),3. Late stage of blastula (13.5 hours),4. Start of gastrula stage (3.5 days),5. Embryo is about 3.1 mm with the initiatives of eyes (7.5 days),6. Embryo is 5 mm, the heart starts to beat (12 days),7. Embryo is about 7.5 mm and the eye is pigmented (16 days),8. Hatching, when the larva is about 14–14.5 mm (34 days)9. Larva is about 18 mm and the initiative of adipose fin appears (42 days),10. 2/3 of the yolk sack has already been consumed and

larvae gulp air (52 days),11. Length of the larvae is about 21 mm, when the edge of pectoral,

pelvic and caudal fins become serrated (59 days), 2. Yolk-sack is almost entirely pigmented (70 days),13. Yolk-sack is fully consumed (85 days).

Density of fry in rearing tanks may varyfrom 2 000 to 5 000 fry/m2 and water sup-ply should be about 0.5–1 l/sec (Hoitsy,2002).

It is recommended to keep fry rearingdevices in a closed place where air tem-

perature can be controlled. This will en-sure a continuous (uninterrupted) growthof fry. Otherwise daily and occasionalsharp changes in temperature may alsoinfluence water temperature of thedensely stocked rearing tanks.


Figure 10: Typical fry rearingfibreglass tank

Figure 11: Typical fry rearingconcrete tanks

� REFERENCES

Allaby, M. 1994 – The Concise OxfordDictionary of Ecology, OxfordUniversity Press

Bascinar, N. and I Okumus, 2004 – TheEarly Development of Brook TroutSalvelinus fontinalis (Mitchill):Survival and Growth Rate ofAlevins, Turkish Journal of Veteri-nary and Animal Sciencies, TheScientific and TechnologicalResearch Council of Turkey,Ankara, Turkey

Bond, C.E., 1996 – Biology of Fishes,Saunders College Publishing,Orlando, Florida, 750p.

Edwards, D. 1989 – Training Course inColdwater fish Culture, TechnicalCooperation Programme, Lectures

delivered at Kalerdasht SalmonidHatchery, Iran, 18 January-3March 1988,http://www.fao.org/docrep/field/003/AC096E/AC096E00.htm

Hoitsy, Gy., 2002 – A Pisztrángtenyésztése és horgászata,152 oldal

Thain, M. and M. Hickman, 1980 – ThePenguin dictionary of biology,Penguin Books

Woynarovich, E and L. Horváth, 1980 –The Artificial Propagation ofWarm-water Fish Species – Amanual for Extension,FAO Fisheries Technical PapersNo. 201, 183p.

� GLOSSARY

Anadromous fishesThose fish species which migrate frommarine to freshwater waters for spawn -ing, like trout or salmon are anadro-mous fishes.

Animal poleIt is the more active, multiplying pole ofan egg cell.

Artificial propagation or reproductionof fishIt is a collective term and comprises awide range of different techniques andtechnologies which aim to produce youngfish under controlled farm conditions.

Elements of artificial reproduction of fishmay be:

� Stripping of wild males and femalesduring spawning season.

� Rearing of broodfish (females andmales).

� Synchronized, stimulated or induc edspawning of females and males.

� Striping and fertilization of eggs throughstimulated or induced ovulation.

� Incubation of embryo and non-feedinglarvae (yolk-sack fry) under controlledfish hatchery conditions.

Depending on the produced fish speciespracticed techniques may include onlysome or all of the listed elements.

BWIt is the abbreviation of body weight.

Catadromous fishesThose fish species which migrate forspawning from freshwater to marinewater, like eel are catadromous fishes.

Changing the colour of fertilised eggsOn fish farms where removing of unfer-tile eggs is done with photo sensorbased machines, carote noids are add -ed to the feed of females. Caro te noidschange the colour of fertile eggs to dark

orange. The machine can more easilydistinguish this colour from the white un-fertile eggs. Therefore, the efficiency ofsorting machines will increase.

ChromosomeIt is a thread-like structure found in allliving cells that carry genetic informa-tion in the form of genes.

Daydegree (Do)It is used to express the length of incu-bation or developmental period of non-feeding larvae. It is the summed upvalue of daily average temperature ofwater. If the actual water temperatureis lower more, if it is higher less daysare needed for the development of em-bryo or non-feeding larvae.

Diadromous fishesThose fish species which migrate forspawning from marine to freshwater wa-ters or vice versa are diadromousspecies. Fish like eel which migrate fromfreshwater to sea water are catadro-mous, while species like trout or salmonwhich migrate from the sea to the fresh-water to spawn are anadromous fishes.

DiapauseSuspended development of an organ-ism. It may occur if environmental con-ditions change to unfavourable.

DOIt is the abbreviation of dissolved oxy-gen in the water which ensures respira-tion of fish. The actual oxygen contentof water depends on some importantphysical and chemical characteristics ofwater.Water can dissolve only a certainquantity of oxygen at a certain temper-ature. The possible maximum dissolvedoxygen content of water (100 percentsaturation) depends on the actual watertemperature and the partial pressure ofoxygen in the atmosphere. Dissolvedoxygen content changes slightly withthe quality and quantity of other dis-solved materials. Altitude also modifiesthe oxygen content of water.

Dormant (resting) stageAt this development stage eggs areready for final maturation and ovulation.During this stage females are waitingfor favourable environmental con ditionsof spawning. When suitable conditionsarrive this stage ends and final matu-ration and ovulation of eggs occur.


References / Glossary 19

EndocrineIt is the collective name of glands whichproduce hormones or hormone* likeproducts and secrete them directly intothe blood system.

FecundityEgg production capacity of a female fish.

FertilizationIt is the act when the male reproductiveproduct, in case of fish sperm entersinto an egg and initiates the division ofthe cell.

FollicleIt is a sheath, protective covering andconnective tissue around egg cells. Itsfunction is to protect and nurture de-veloping eggs, eventually become adouble layer of eggs (Woynarovich andHorvath, 1980).

GametesThey are mature haploid* female (ovu-lated egg) or male (sperm) germ cells.They are able to unite into zygote* withanother reproductive cell of the oppo-site sex.

GenotypeIt is the genetic constitution of living or-ganisms.

Germinal diskIt is the location on the top of the yolkwhere an egg cell is fertilized and cell-division starts.

GlobulinsThese are simple proteins soluble insalt solutions.

GnRH/AGonadotropin releasing hormones aresecreted by the hypothalamus when fishreceive a favourable environmentalstimuli for spawning through their re-ceptors and brain. These hormones, astheir name indicates stimulate the re-lease of gonadotropin hormones in the

pituitary. GnRH/A is the abbreviation ofgonadotropin releasing hormone ana-logues which are artificially pro duced inorder to induce ovulation and sperma-tion in a female or male fish.

GonadsIn bony fishes gonads, ovary and testisare paired and in most forms there is noconnection between the reproductiveand urinary systems (Bond, 1996). Introut the two systems connect into onejoint urogenital papilla where they empty.

The gonads develop from the peri-toneum in which primitive egg cells canbe found.

HabitatIt is the environment of an organism orcommunity, characterized by its physi-cal or biotic properties (Allaby, 1994).

HaploidA haploid cell is a germ cell which has anunpaired, single set of chromosomes*.

HormoneIt is produced by specialised glands inorder to regulate action of organs suchas gonads.

Hypophysis or pituitaryIt is a very important endocrine glandunder the brain. It produces differenthormones, among others gonado tro -pins which stimulate and control theactivity of gonads. This gland of sexu-ally matured male and female pre-served with alcohol or acetone areused for inducing ovulation or sperma-tion in female and male fish.

HypothalamusIt is a region of the brain under the thal-amus through which fish receive andpass sensory information.

LacustrineA fish species is lacustrine if it is adapt edto lake habitat*.

oC

1

2

3

4

5

DO(mg/l)

13.92

13.52

13.20

12.88

12.52

oC

6

7

8

9

10

DO(mg/l)

12.21

11.91

11.62

11.33

10.10

oC

11

12

13

14

15

DO(mg/l)

10.83

10.61

10.38

10.15

9.96

oC

16

17

18

19

20

DO(mg/l)

9.75

9.55

9.35

9.16

9.00

oC

21

22

23

24

25

DO(mg/l)

8.82

8.67

8.41

8.36

8.22

Table 5:Dissolved oxygen

content of fullysaturated water

at differenttemperatures

MeiosisIt is a type of cell division that results indaughter cells with half of the numberof chromosomes as the parent cell.

MitosisIt is a type of cell division that results indaughter cells which have the samenumber and kind of chromosomes asthe parent cell.

Neuro-endocrine processIt is the response of sexually maturedfish to favourable environmental stimulicarried by the receptors to the brain. Asa result the brain together with the en-docrine system executes the develop-ment and release of eggs and sperms.The schematic sequence of informationis: 1) Favourable environmental condi-tions → 2) Receptors → 3) Brain → 4)Hypothalamus that acts through go-nadotropin releasing hormones (GnRH)→ 5) Pituitary that acts through go-nadotropin hormones (GtH) → 6) Go-nads → 7) Secondary and accessorysex characteristics; reproductive behav-iour and activity (Woynarovich and Hor-vath, 1980; Bond, 1996).

OvaryIt is the female reproductive organwhich produces eggs.

OvulationIt is the release of matured eggs fromthe ovary.

Parental careParental care of egg laying bony fishesmay be indirect, direct and the combina-tion of these two. At indirect parental careparents select the type of spawningground where released and fertilizedeggs and hatched larvae can safely de-velop and feeding larvae and developingfry can find both food and shelter. A char-acteristic of these fish species is that theirfecundity is very high. Their females pro-duce several hundred thousands ofeggs. This ensures the survival of suffi-cient offsprings required for the mainte-nance of the species. Substratespawning common carp, breams, pikeand river spawning Chinese and Indianmajor carp and South American Caras-sius species are typical members of thisgroup of cultured freshwater fishes.There are freshwater fish species whichperform active parental care during incu-

bation of eggs but then they abandon thehatched larvae. They wash out or buildnests where developing eggs are venti-lated and guarded. European catfish andpikeperch belong to this group of fish. Fe-cundity of these fish is also high. Fishspecies of active parental care produceless eggs. As a compensation they takeintensive care of the developing eggs,hatched larvae and even the fry. Themost well known representatives of sub-strate spawning and mouth breedergroups of freshwater fishes are tilapias.

PeristalticIt is constrictions and relaxations ofmuscles of the intestine or other canal-type organs. This is an unintentionalwaive-like movement which pushes thecontent of the canal forwards.

PhenotypeIt is the observable characteristics ofinteractions between genotype and en-vironment.

PituitarySee at hypophysis.

Primary oocytesThey are egg cells which develop fromprimitive egg cells with normal mitosis*.

RiverineA fish species is riverine if it is ad apt edto a river habitat*.

SaprolegniaThe fungi responsible for saprolegnia-sis are secondary pathogens which ap-pear and develop after handling or anytraumatic damage caused to the skinof a fish.

Symptoms caused by Saprolegnia spp. aregreyish-white patches on the skin whichhave a cotton wool-like appearanceunder the water.

StrippingIt is the act of removing ovulated eggsand milt from female and male fish.

TestisIt is the organ which produces sperm.Vegetal poleAlso called vegetative pole. It is the lessactive yolky pole of an egg cell.

VitellogenesisIt is a longer process before each re-productive season when the yolk buildsinto the eggs.

ZygoteIt is the name of fertilized eggs


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