Guide to the Small Scale Artificial Propagation of Trout

Home , Coldwater fish, Milt, Papilla (fish anatomy)

GUIDE TO THE SMALL SCALE ARTIFICIAL PROPAGATION OF TROUT Authors: GYÖRGY HOITSY, ANDRÁS WOYNAROVICH and THOMAS MOTH-POULSEN GUIDE TO THE SMALL SCALE ARTIFICIAL PROPAGATION OF TROUT

Authors: GYÖRGY HOITSY, ANDRÁS WOYNAROVICH and THOMAS MOTH-POULSEN

Budapest, 2012 2

Photos and illustrations by courtesy of GYÖRGY HOITSY

The designations employed and the presentation of material in this 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 or development status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. The mention of specific companies or products of manufacturers, whether or not these have been patented, does not imply that these have been endorsed or recommended by FAO in preference to others of a similar nature that are not mentioned. The views expressed in this information product are those of the author(s) and do not necessarily reflect the views of FAO. 3

PREFACE This book aims to provide basic information on reproduction and propagation of trout, tries to describe most important hatchery activities and challenges and also provides advices on the rearing of trout fry in order to support small scale farmers and pro- ducers. As small scale fish farming is a substantial opportunity to generate income and also provides a valuable protein source it is important to afford knowledge about the proper technology.

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

Thanks are also due to Mr. ISTVÁN FÁBIÁN (www.ajel.hu and [email protected]) for the typographical design and work of this publication. 4 SMALL SCALE ARTIFICAL PROPAGATION OF TROUT

TABLE Preface 3 OF CONTENTS Acknowledgement 3 1 Introduction 5 2 Reproduction of trout in the nature 5 2.1 Reproduction strategy 5 2.1.1 Reproductive age and number of times spawning occurs in a lifetime 5 2.1.2 Fecundity 6 2.1.3 Size of eggs 6 2.1.4 Reproductive behavior 6 2.2 Spawning 7 3 Reproduction of trout in fish farms 8 3.1 Preparation for propagation 8 3.2 Rearing and feeding of brood fish 10 3.3 Preparation of the hatchery 10 3.4 Works in the hatchery 11 3.4.1 Selection of suitable broodfish and stripping of eggs and milt 11 3.4.2 Incubation of eggs 14 3.4.3 Hatching and development of sack-fry 15 3.4.4 Rearing of fry 16 References 17 Glossary 18

Tables Table 1: Reproductive age and period of selected trout species 5 Table 2: Size at sexual maturation, fecundity and duration of eggs and sack-fry incubation of selected trout species 6 Table 3: Key propagation data of brown and rainbow trout 13 Table 4: Length of the incubation period of trout eggs under different water temperatures 15 Table 5: Dissolved oxygen content of fully saturated water at different temperatures 19 Figures Figure 1: Differences between females and males during reproductive season 9 Figure 2: Hand stripping of a female 12 Figure 3: Stripping of milt onto eggs 12 Figure 4: Fertilization (mixing of eggs with milt) 12 Figure 5: Adding water to fertilized eggs 12 Figure 6: Eyed eggs 12 Figure 7: Hatched larvae 12 Figure 8: Different incubation vessels for trout eggs and larvae 14 Figure 9: Development of fertilised rainbow trout eggs and hatched larvae at about 10 oC16 Figure 10: Typical fry rearing fibreglass tank 17 Figure 11: Typical fry rearing tanks 17 Boxes Box 1: Development and ovulation of eggs in sexually matured bony fish 7 Box 2: Structure of trout egg and sperm 11 Introduction / Reproduction of trout in the nature 5

1 INTRODUCTION 2 REPRODUCTION OF TROUT Small scale trout farming is a realistic in- IN THE NATURE come generating alternative in the moun- tainous regions of Central and Eastern Europe, the Caucasus and Central Asia where income sources and employment 2.1 REPRODUCTION opportunities are scarce or even missing. STRATEGY Though all female eyed eggs of well performing pedigree trout strains can be Not only growth but also the successful purchased from many different locations reproduction of fish depends on the sur- of the world propagation of locally main- rounding environment. For this reason tained trout can still be technically and different species of fish develop and economically feasible. Increased official practice different reproductive strategies opposing of introducing fish strains with which, in a characteristic way to species, genotypes new in a region is also an ad- ensure a successful offspring production ditional reason why practical knowledge of even under fluctuating environmental artificial reproduction of rainbow trout may conditions. be very useful. Reproductive strategy of fish includes It is expected that technical information reproductive age, fecundity according to presented in this book will help in the re- size and age, size of eggs, reproductive production of other trout species. It may behavior and the number of times spawn- also successfully complement recently ing occurs in the lifetime of females (Bond, produced FAO publications such as Small 1996). scale rainbow trout farming, Small scale trout processing methods and Trout farming based angling tourism. 2.1.1 Reproductive age and In order to satisfy interests for further the number of times spawning details a glossary is compiled and tables and annexes are attached to this paper. occurs in a lifetime For the sake of finding additional information asterisk symbols (*) are used after In different fish species the length of time in words in italics which are explained in the which males and females become sexually glossary. mature may vary between a few months and several years. The actual sexual mat- Table 1: uration of trout depends on spe cies, sex Reproductive age and environmental conditions (water tem- and period perature, feeding conditions, etc.) in which of selected trout fish live and develop (see Table 1). species

Sexual maturation Reproductive period (years) (years)

Species In nature Within farm conditions Within farm conditions

Females Males Females Males Females Males

Rainbow trout 3–4 2–3 2–3 (1)–2 4–6 6–7 Brown trout 3–4 2–3 3 2 4–6 6–7 Brook trout 3–4 2–3 2–3 (1)–2 2–3 2–3 6 SMALL SCALE ARTIFICAL PROPAGATION OF TROUT

2.1.2 Fecundity

Fecundity* of egg-laying bony fish species depends on their parental care* and the size of produced eggs. Fecundity of fish is expressed with the absolute and relative number and the weight of eggs produced Table 2: Source: by a female. Table 2 summarises the fe- Size at sexual maturation, fecundity and 1. Bascinar and cundity of widely and frequently produced duration of egg and sack-fry incubation of Okumus, 2004, trout species. selected trout species

Size of Fecundity of female Duration (Do) broodfish (1000 eggs) Incubation of egg Species Females Males Absolute Relative Up to eyed-egg Swim-up Total (kg) (kg) (egg/fish) (egg/kg BW*) stage

Rainbow trout 1–7 1–4 1–10 1.6–3.0 1601 3101 5001 Brown trout 1–6 1–4 0.5–8 1.6–3.6 195–2731 250–4061 380–6101 Brook trout 1–3 1–1.5 0.5–5 1.2–2.5 195–2761 235–4441 338–6751

2.1.3 Size of eggs At trout reproductive behavior includes timing of spawning, selection and prepa- Egg sizes of fish indicate the size of yolk- ration of spawning ground, courting and sack in developing embryos and non- mating with selected males. feeding larvae which are also called By mating season eggs and milt should sack-fry (see Figures 9). be ripe, ready for being fertilized (eggs) or Salmonid eggs are the largest among to fertilize (milt). Spawning in the right the eggs of bony fishes. The size of their place and time when both eggs and milt dry eggs varies between 3.7 and 5.2 mm are ripe and all environmental conditions (32–100 mg) (Hoitsy, 2002). Egg size of are favourable is the final response of the younger and smaller females may be endocrine* system of fish to environmen- smaller than that of the elder and larger tal cues.These are physical (temperature, ones. Eggs of 5–6 year-old females are clearness, speed and depth of water) and the largest but the quality and quantity of chemical (clean water, rich in oxygen) feed also influences the actual size of qualities of water, light, day-length, suit- them The volume of 1 000 eggs may be ability of mating ground and presence of 79–90 cm3. the opposite sex (Woynarovich and Hor- The large size of trout eggs can be ex- vath, 1980 and Bond, 1996). In other plained with the long duration of egg and words favourable environmental condi- sack-fry incubation. tions stimulate production, development, final maturation and ovulation of eggs (see Box 1). 2.1.4 Reproductive behavior Development and release of milt in males is also influenced by environmental conditions but nature built less endocrine Reproductive behaviour is a complex se- control into this process than into the one quence of sexually mature female and for females. male fish which aims to ensure the high- est possible survival of laid and fertilised eggs and hatched non-feeding larvae. Reproduction of trout in the nature 7

2.2 SPAWNING Development and ovulation* of eggs Most of the trout species are diadromous*, in sexually matured bony fish more precisely anadromous* fishes. Still, those riverine* and lacustrine* trout spe- By about the first months after swim-up and starting exter- cies which habituated fully to freshwater nal feeding of young fish fibre-like initials of the gonads* environment, hence never move into the (ovary* and testis*) are already formed. seas, also migrate for spawning to upper In this stage the ovary already contains the primitive egg sections of rivers and their tributaries. cells (oogonium, ovogonium or archovogonium) from which Shortening days and decreasing water the eggs will develop when the fish reaches sexual matura- temperature affect hormone concentration tion. Evidence of sexual maturation is when a first produc- of brood fish. This causes rhe develop- tion cycle of eggs suitable for ovulation and fertilization* ment of secondary and accessory sex occurs. Development of egg batches in the ovary before characteristics, drives reproductive beha- each spawning is a precondition of successful reproduction. viour and triggers reproductive activities. This process has different subsequence phases: Light conditions have a very important 1. A batch of primitive egg cells (oogonia) in the ovary role in the reproductive behaviour and ac- transforms into primary oocytes*. tivity of trout. Shortening days stimulate 2. A follicle* is formed around each primary oocytes. development of eggs and activate in- 3. Eggs undergo a quantitative development called vitello- stincts of spawning migration. On large genesis* when yolk builds into the eggs in four subse- broodfish farms where the objective is a quent steps. This phase is a longer procedure which is continuous, year-round propagation and completed before the spawning season. During vitello- eyed-egg production light conditions are genesis a properly balanced feeding of females is es- also controlled in order to stimulate and sential. synchronize ovulation in females. 4. Though eggs are ready for final maturation and ovula- Changes of water temperature also pri- tion when the vitellogenesis is completed still there is a marily stimulate and synchronise ovula- dormant (resting) stage* in their development. The rea- tion in females. If it decreases autumn son for it is that the future of fertilized eggs depends on spawning strains, while if increases spring the timing of spawning when environmental conditions spawning strains will prepare for spawn- are most suitable for laid and fertilized eggs. ing. If season specific trend of water tem- 5. Dormant phase of eggs in the ovary ends when environ- perature changes (increase in autumn mental conditions become favourable for spawning. At and decrease in spring) preparation for this time favourable environmental stimuli arrive into the spawning will stop. brain of fish through sense organs. A complex neuro-en- Dissolved oxygen (DO*) content of docrine process* starts in the brain which results in the water is also a prime environmental con- ovulation of eggs and spawning of fish. dition which drives and influences the Depending on fish species the above described procedure spawning of trout. Trout are mostly autumn may be continuous within a well defined shorter or longer spawning fishes since they are the most period of the year or it can be seasonal as it is in case of DO demanding fish species therefore a trout. high DO is needed for the proper devel- After: Woynarovich and Horváth, 1980 opment of their embryos and sack-larvae. This environmental condition will more likely occur during winter as DO content is higher in colder waters. Swim-up of fry is spring. Spawning of trout takes place in Box 1 usually finished by the end of the winter the headwaters and tributary streams of which reduces possible losses that melt- rivers or in the inlet or outlet streams of ing snow and spring floods may cause. lakes (Edwards, 1989). Water current conditions, water depth Spawning of trout is wonderful which and bottom types have less role in the can be observed in cold mountain rivers final maturation and ovulation of eggs. and larger streams where they leave. Fe- For the above described reasons trout males and males swim up to the upper spawn seasonally. Actual spawning sea- sections of rivers and streams and they son depends on species and strains easily pass rapids as high as 0.5–1 meter. hence it might be either in autumn or in They swim in the dark during evening and 8 SMALL SCALE ARTIFICAL PROPAGATION OF TROUT

night time in order to reach their spawn- 3. REPRODUCTION ing ground by dawn. At the spawning ground females OF TROUT choose the most suitable location where the bottom is covered with pebbles and IN FISH FARMS the water is swift. Here they make their shallow nests (also called redd) by clean- Trout becomes sexually mature in fish ing an area of about 0.5–1 meter diame- farms sometimes even earlier than in na- ter. These hollows on the bottom of ture if water temperature is higher and streams and rivers indicate the presence feeding is better than there. of an active trout population. When nests As many other fish species, trout also are ready their bright clean pebbles will can reach sexual maturation in fish farms. contrast with surrounding bottom covered Females and males will produce eggs and with greenish or brownish algae. milt (gametes*) but they can not spawn Males follow females. This time they successfully under regular fish farm con- are aggressive and fight for females. The ditions unless all required favourable en- strongest male occupies the nest with the vironmental conditions are simulated. female where they mate in the early hours Though, reliable production of large quan- of the day. tities of fertile eggs and hatched larvae At mating the female stops in the front would be both difficult and expensive on while the male stands behind her. Then this way. Therefore, there are other more the female bends in a “C” shape and efficient ways of artificial propagation*of presses the ovulated eggs out with a peri- trout which result in the ovulation of eggs staltic* movement of her muscles. When stripped and fertilized with milt from the female positions herself and is pre- males. pared to release the eggs the male joins. He also bands in a “C” shape close to the side of the female and fertilizes the re- 3.1 PREPARATION FOR leased eggs. They have to be fast and ac- PROPAGATION curate because only a very short period of time (sometimes even seconds) is avail- On a fish farm the sign of the arriving able to fertilize the released eggs which propagation season is that sexually ma- are quickly drifted away by currents. tured females and males gather at the in- One spawning nest may be used by flow of their tank near to the water surface more than one couple. Trout do not guard and often try to jump against the water their nests but males may remain around current. This indicates that females and and chase away intruding fishes. Later males are ready to migrate to spawning they also leave the site. grounds. At this time females and males Some publications of trout spawning should be separated. Otherwise already describe trout as a fish which covers its ripened brood fish will spontaneously eggs with fine pebbles or even by sand. spawn while others will pick and consume This is incorrect because trout has the released and fertilised eggs from the bot- most oxygen-demanding eggs therefore tom of the tank where this uncontrolled any action to cover and hence cut them off spawning takes place. from open, oxygen rich water currents is In trout sexes can easily be distin- rather unlikely. guished during the propagation season (see Figure 1). Therefore separation of females and males can be safely completed: Males are slimmer and their back is higher and humpy. Their colours are brighter. Their lower jaw is pointed and wedge shaped. At elder age lower jaw takes a hook shape and is covered with Reproduction of trout in fish farms 9 swollen growths. Their pointed urogenital stimulate both final maturation and ovula- papilla sticks out from which white milk- tion of eggs in females. If a fish farm is type sperm bursts if the abdomen is gen- successful in the simulation of most im- tly pressed. portant favourable environmental condi- Females are more round and filled at tions then less fishing and handling efforts the belly because of their enlarged ovary. will result in a higher quantity and better Their urogenital papilla sticks out about 1– quality egg production. This will also save 2 cm and is top is rounded (see Figure 1). brood fish from unnecessary stresses Fishing and sorting of brood fish when their readiness is checked. should be done gently with care in order The best way for simulation of favour- not to stress and hurt the fish which are able environmental conditions is when full of eggs and milt. water level is lowered and speed of water On large tout farms which are special- is increased in freshly cleaned tanks ized on propagation, ovulation and sper- where females and males are separated. If miation are induced with hormones such as it is done properly, about 50–70 percent of salmon hypophysis* or Gonadotropin Re- females will be ready for stripping 7–10 leasing Hormone Analogues (GnRH/A*). days after their separation. In case of au- However, most of small scale trout farms tumn spawning females a slight reduction, Figure 1: do not use hormones to harmonise and in case of spring spawning females a slight Differences between complete ovulation in females and sper- increase of water temperature is also an females and males miation in males. These fish farms imitate effective way to imitate environmental con- during reproductive favourable environmental conditions which ditions which will advance ovulation. season

Those females which do not react on the described manipulation of keeping conditions will perform a lengthy propagation period when a successful stripping will remain less predictable. 10 SMALL SCALE ARTIFICAL PROPAGATION OF TROUT

3.2 REARING AND also be suitable to change water in it about FEEDING OF BROOD FISH 2–10 times per day. On many fish farms males and females are kept separately during the entire year. If eggs, fry or young fish are not pur- Such practice has no considerable ad- chased but are produced on a fish farm vantages if basic reproduction related the entire success depends on the quality physiological and ethological aspects are of brood stock which is kept and propa- in focus. It is true that males and females gated there. Only those healthy females should be separated before the propaga- and males should be propagated which tion season. Still, some young males have a proven good life time performance placed in the tank of females before prop- and are able to inherit them. Most advan- agation will help advancing and synchro- tageous traits are size, utilization of feeds, nizing ovulation in females. Even after the growth rate and overall resistance to most proper stripping* of a female a little stress and diseases. portion of ovulated eggs will remain in the It is a general rule for a positive selec- fish. If females cannot release these eggs tion of brood fish that good genotypes* and they remain in the fish they will nega- should be searched among fish with good tively influence egg production next year phenotypes*. It means that when a fish is and eggs remained in the female may selected for propagation its appearance, decay and even cause mortalities. There- physiological properties and individual fore, if these females are kept together performance should be considered. with males they will drive out even the last It is advantageous to select future drops of eggs from them. Males are very brood fish from a stock which is about 10 aggressive during the propagation sea- month old. The most properly looking, son. If females are mixed with males after largest and healthiest specimens from the stripping, aggressiveness of males will re- same age group should be selected for fu- duce. Therefore, losses due to fighting ture propagations. From this time on se- and wounds will reduce too. lected and separated stocks of future brood fish should receive a different, less protein rich diet. If fish receive high protein 3.3 PREPARATION diet their muscles and body will grow in- OF THE HATCHERY stead of their gonads.Today well balanced feeds are widely available for this purpose Parallel to separation and preparation of where all the proteins, energy, vitamins brood fish for propagation fish hatcheries and minerals are contained in the right should also be prepared. It means: quantity and proportion needed for grow- Checking, repairing and cleaning of ing and grown-up brood fish. Sometimes both water supply and drainage sys- also other ingredients are added in order tems. to *. change the colour of the fertilized eggs Cleaning of brood fish tanks, trolleys, Under farm conditions male trout be- hatchery devices and equipment. come sexually mature in the second year, Making ready weighing and measuring while females in the thirds year with the devices. exception of brook trout. About 60–70 per- Completing and cleaning stripping cent of brook trout females become sexu- bowls and towels. ally mature already by the second year. In nature both males and females need 1–2 Disinfection of the water supply and more years to reach sexual maturity. drainage systems and hatchery devices About 6–7 brood fish should be stocked can be done with formalin. per 1 m2 of tank area. There are no specific criterions of a good brood stock rearing or keeping tank. It should be suitable for being cleaned and kept cleaned easily to avoid accumulation of faeces and unconsumed feeds. It should Reproduction of trout in fish farms 11

3.4 WORKS of fish allows driving the ovulated eggs IN THE HATCHERY with a gentle massage with the thumb and forefinger toward the urogenital opening from where eggs will directly pour into the Works in the hatchery include the choos- stripping bowl. ing of suitable broodfish, stripping, fertil- In case of rough handling and unpro- ization and incubation of eggs and rearing fessional stripping fish may be hurt or of hatched fry. even injured. Therefore, instead of stripping everywhere from head to tail it should be restricted only to the lower section of 3.4.1 Selection of suitable the belly. The stripping hand should not broodfish and stripping of eggs start higher than an imaginary line be- and milt tween the dorsal and the pelvic fins. If fish is stripped above the mentioned imagi- There are different techniques for remov- nary line its internal organs such as ing ovulated eggs and milt from broodfish. spleen or liver may be damaged which Elaboration of the first technique of artifi- can result in mortality. Another reason why cial propagation of trout copied natural females should be stripped at the lower spawning. It was done by a German fish section of their bellies is that the ovulation farmer, Jacobi between 1763 and 1765. of eggs starts in the lower section of the He stripped eggs into a jar of water. Today ovary. Hence, there is no reason for strip- nobody follows this “wet” technique be- ping fish along the entire body. cause the expectable rate of fertilization is Milt of males is stripped similarly to as low as 20 percent. eggs. Gentle handling and stripping is In 1856 Vranszkij Russian fish culturist very important here, too. Box 2 started a “dry” technique. Since this time this method has been successfully practiced because it ensures 98–100 percent fertiliza- Structure of trout egg and sperm tion. The essence of this technique is that first eggs then milt are stripped into a dry Egg: It has an animal pole* and a vegetal pole*. Egg shell of bowl where they are gently mixed before fer- brown trout is about 33–37 microns thick while this is thin- tilization starts with the adding of water. ner at rainbow trout. On the egg shell about 1 micron pores The first step is the separation of those can be observed which continue in narrow ducts. Microphyle females which already ovulated. Signs of through which sperm enters is situated on the animal pole ovulation are an enlarged and softened ab- of the egg. After the first sperm enters it closes but without domen. Eggs in the female can be felt when the entering of any sperm the microphyle will also close gently touching and the urogenital opening within about a minute when the egg starts swelling. Periv- sticks out about 1-2 cm (see Figure 1). itelline space separates shell from the cell which fills with There are different techniques for strip- fluid within 20–60 minutes after fertilization. This fluid filled ping ovulated eggs. According to the Aus- space allows the embryo to rotate (gyrate) freely in the egg tralian one air is pumped into fish with a shell and to remain always in the right position. During syringe and this is what presses eggs out swelling the volume of egg increases with about 12–20 per- of the female. The Swedish technique cent. Trout egg is not adhesive but may stick to a substrate uses a double walled rubber pipe. Female or to the wall of the hatchery devices until fully swelled. is placed into this tube then water is in- Getting into the egg the germinal disk*, the vitelline mem- jected between the walls of the tube. The brane and yolk can be found. The yolk is a dense yellowish inner soft wall covers the entire body liquid which contains globulin* and oil droplets. These oil which gently presses out the ovulated droplets accumulate in the upper animal pole of the egg in eggs from the female. order to keep the germinal disk at the right place and in the A most widely practiced technique is correct position. hand stripping. This technique is simple. Sperm: Head of the sperm is 1.7 by 2 microns and its tail Head and tail of fish are wrapped into is about 25–35 microns long. Active life of sperm starts when handtowels and the female is firmly but ejaculated into water and lasts for about 24–40 and 40–50 gently hold at her two “ends” on a way that seconds at brown trout and rainbow trout, respectively. head is 45 degree upward. This position 12 SMALL SCALE ARTIFICAL PROPAGATION OF TROUT

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

Quick and gentle stripping of eggs is ping bowl or they are steered and mixed essential. Where larger quantities of fe- with milt roughly they may loose their fer- males are stripped MS 222 tranquilliser is tility and eggs will die. used. Recently alternative, less expensive Trout ovulate in batches with intervals. materials are researched and used, About 2-5 days after the first major ovula- among others clove oil. tion when about 75-85 percent of the eggs Not only brood fish but also stripped can be stripped a smaller second ovulation eggs should be handled with care. If they occurs. For this reason it is important either fall from a higher distance into the strip- to check the already stripped females and Reproduction of trout in fish farms 13 strip them again or to place them together Therefore, before stripping fish - espe- with males. They will drive out later ovu- cially their urogenital opening - should be lated eggs from the females. Otherwise dried with a towel. ovulated but not stripped or released eggs One portion of stripped eggs, about 5 will decay in the fish. Even if this process 000-10 000 pieces should be fertilised would not necessarily cause mortality, still with the milt of at least 2 or 3 males. This it will negatively influence the quality and will ensure proper fertilization of all eggs quantity of egg production in the next year. even if, for some reasons, one of the About 4-6 year old and 2.5-3.5 kg large males is unfertile. Males can be stripped females will produce the largest quantity again after about 3-7 days. Therefore milt and best quality eggs. Egg production of of good males can be used for the fertil- elder than 6-year-old females will gradu- ization of eggs from many different fe- ally reduce both quantitatively and quali- males. 1 male is enough to fertilize the tatively because of the accumulated effect eggs of about 3-8 females. of different stresses experienced by fish. After stripping, eggs and milt should It is very important to avoid the contact be gently mixed still without water. If all of eggs with water before fertilization. eggs are covered with the film of milt they

Brown trout Rainbow trout (Salmo trutta m. fario) (Oncorhynchus mykiss)

Sexual maturation of females (years): 3 Sexual maturation of males (years): 2 Proportion of sexes: 3–8 ♀:1 ♂

Propagation season: November–January November–March (depending on the strain)

Eggs per 1 kg BW (No.): 1 600–3 580 1 600–3 100 Eggs in 1 kg of dry eggs (No.): 12 500–16 500 10 000–18 200 Quantity of milt per male (cm3): 5–27 Quantity of sperm in 1 cm3 milt: 16 000 000 20 000 000 Fertility rate of eggs (%): 95–100 85–100 Rate of hatching from fertilized eggs (%): 90–100 75–95 Length of embryogenesis at 10 °C (days): 40–42 30–34 Duration until eyed-egg stage at 10 °C (days): 20–21 18–21 Duration of sack-fry (none-feeding larvae) stage (days): 20–28 20–21

Table 3: should be left for about 1-2 minutes in Key propagation order to let them be fertilized. When eggs data of brown and are fertilized a little fresh water should be rainbow trout added then eggs should be gently washed clean with adding more fresh water to them. During this procedure bad, unfertile (white) eggs should be removed. They are white because proteins coagu- late in the unfertile eggs. After washing and cleaning eggs should be placed into hatchery devices. 14 SMALL SCALE ARTIFICAL PROPAGATION OF TROUT

3.4.2 Incubation of eggs hours. Then the first sensitive period starts and lasts until eyed-egg stage. During this During the last centuries many dozens of period multiplying cells in the eggs are different types of incubation vessels were very fragile. A bigger bump on the egg invented, developed and used. They were may cause a malformation in the develop- different both in materials (ceramic, glass, ing embryo or even mortality. Therefore wood, metal or plastic) and shape. Today developing eggs should be kept undis- Californian, Sandfort and vertical tray in- turbed in hatchery devices. After eyed-egg cubators are used most widely (see Fig- stage until hatching eggs can be trans- ure 8) but cylindrical Zuger jars can also ported, hand or machine sorted again and be found in many trout hatcheries. bad, damaged eggs can also be picked When eggs are placed into incubation out. It is because eggs are hardy during vessels - about 10 000 eggs/0.2 m2 - they this period. Then from about 48 hours be- are less sensitive and bad ones should be fore hatching they become fragile again. picked out for until about an additional 36 During the first fragile period of eggs the only prevention against saprolegnia* is the use of formalin in a concentration of about 0.25 ml/l. The use of specific iodine containing products is also feasible against saprolegnia. Since saprolegnia develops on dead and decaying eggs from which it can spread to healthy ones it is very important to remove damaged and dead eggs as soon as they can be touched, regardless if they are infected with saprolegnia or not. There are contradicting opinions and publications about light sensitivity of trout eggs. It is sure that most of trout eggs ex- posed to direct sunlight for a few minutes will die. Therefore diffused light or even Figure 8: darkness in the hatchery is widely recom- Different incubation mended. vessels for trout eggs and larvae 1. Californian hatchery, 2. Sandfort hatchery tray and 3. Vertical tray incubator Reproduction of trout in fish farms 15

3.4.3 Hatching and Larvae are hatched with a large yolk- development of sack-fry sack from which they feed until switching to external feeding. Yolk-sack might make The actual time of hatching depends on up for 2/3–3/4 of the entire weight of water temperature but oxygen content of hatched larvae. water also greatly influences it. Hatching Hatched larvae remain laying on the below 4 oC and above 15–18 oC can only bottom of hatchery devices. Under nor- be done with great losses. mal conditions they evenly occupy these. Eggs of rainbow trout and brown trout During incubation of non-feeding larvae will hatch within about 520 and 320 day- egg shells, dead larvae, floating grease degrees* (Do). If in nature water tempera- and oil drops should be removed from ture is less than 2 oC, the development of water surface. Developing non-feeding embryos stops. This diapause* causes larvae does not need any other care for great losses. It is especially important be- about 2–4 weeks (see exact duration in cause in nature, even if all environmental Figure 9). During this period only dead conditions are optimal not more than 15– larvae should be removed regularly from 20 percent of eggs will hatch and only the devices. 0.5–1 percent of fertilized eggs will survive It is important not to expose develop- and grow to sexually mature adults. ing larvae to strong light since then they After fertilization, at the start of cell-divi- will try to hide under each other which sion, at pigmentation of the eyes and before may cause oxygen shortage, hence mor- hatching oxygen demand of de ve loping tality. It is also important to keep the rear- embryos will especially increase. During ing devices clean. This is done by an these periods insufficient quantity of oxygen appropriate exchange of fresh water and will result in higher mortality or at the end of siphoning of dead and decaying larvae. the embryonic stage as a result of oxygen During this period larvae are sensitive to deficiency earlier hatching will occur. chemicals including formalin, therefore a Before hatching embryos gradually clean rearing environment is the only op- move (gyrate) more and more intensively. tion for prevention. This movement mechanically thins the egg As larvae advance in development shell from inside. In addition, hatching lar- their yolk-sack is gradually consumed and vae decompose the egg shell with an en- they start to feed externally. They also zyme (hyaluronidase) which is secreted by start to move until finally they swim up to a gland found in the head of the embryo. the water surface and gulp air from the at- Eggs stripped from different females mosphere. External feeding starts still be- but fertilized at the same time may hatch fore the yolk-sack is entirely consumed. differently. This difference may be 2–3 This few days overlapping of internal days. Hatching larvae tear open the egg (yolk-sack) and external feeding of larvae Table 4: shell with their tail and literally reverse ensures a safe supply of nutriment for Length of the from it. Larvae which tear up the egg shell swim-up fry until they learn how to feed. incubation period of with their head often die because the egg By the time the yolk-sack is fully con- trout eggs under shell remains stuck on their head and gills, sumed fry learn how to feed from their en- different water therefore they die of suffocation. vironment. temperatures

Water Brown trout Rainbow trout Brook trout temperature (oC) Days Do Days Do Days Do

6 77 462 55 330 80 480 8 61 488 43 344 62 496 10 41 410 31 310 40 400 12 27 324 26 312 38 456 16 SMALL SCALE ARTIFICAL PROPAGATION OF TROUT

Figure 9: 3.4.4 Rearing of fry Figure 9: Development of fertilised rainbow trout eggs and hatched larvae at about 10 oC After the swimming-up of fry their feeding 1. Moment of fertilization, should start with properly balanced dry 2. Early stage of blastula (7.5 hours), feeds which contain the needed quality and 3. Late stage of blastula (13.5 hours), quantity of proteins (50–60 percent), vita- 4. Start of gastrula stage (3.5 days), mins and minerals. Size of the applied feed 5. Embryo is about 3.1 mm with the initiatives of eyes (7.5 days), is also very important. It should only be as 6. Embryo is 5 mm, the heart starts to beat (12 days), large as the developing fry can easily grab 7. Embryo is about 7.5 mm and the eye is pigmented (16 days), and swallow. During the rearing of fry or as 8. Hatching, when the larva is about 14–14.5 mm (34 days) often called advanced fry, intervals between 9. Larva is about 18 mm and the initiative of adipose fin appears (42 days), feedings should be about ½ hours. A sign of 10. 2/3 of the yolk sack has already been consumed and insufficient feeding is the increasing differ- larvae gulp air (52 days), ence between individual sizes of developing 11. Length of the larvae is about 21 mm, when the edge of pectoral, fry. This may result in serious cannibalism. pelvic and caudal fins become serrated (59 days), Tanks of different shapes are used for 2. Yolk-sack is almost entirely pigmented (70 days), rearing fry. Few meters long troughs, rec- 13. Yolk-sack is fully consumed (85 days). tangular or round tanks are the most widely applied rearing devices. At the be- ginning depth of water may vary between 0.1 and 0.2 meters which should gradually be increased to 0.5–0.8 meters. Reproduction of trout in fish farms 17

Figure 10: Figure 11: Typical fry rearing Typical fry rearing fibreglass tank concrete tanks

Density of fry in rearing tanks may vary perature can be controlled. This will en- from 2 000 to 5 000 fry/m2 and water sup- sure a continuous (uninterrupted) growth ply should be about 0.5–1 l/sec (Hoitsy, of fry. Otherwise daily and occasional 2002). sharp changes in temperature may also It is recommended to keep fry rearing influence water temperature of the devices in a closed place where air tem- densely stocked rearing tanks.

REFERENCES

Allaby, M. 1994 – The Concise Oxford delivered at Kalerdasht Salmonid Dictionary of Ecology, Oxford Hatchery, Iran, 18 January-3 University Press March 1988, Bascinar, N. and I Okumus, 2004 – The http://www.fao.org/docrep/field/003 Early Development of Brook Trout /AC096E/AC096E00.htm Salvelinus fontinalis (Mitchill): Hoitsy, Gy., 2002 – A Pisztráng Survival and Growth Rate of tenyésztése és horgászata, Alevins, Turkish Journal of Veteri- 152 oldal nary and Animal Sciencies, The Thain, M. and M. Hickman, 1980 – The Scientific and Technological Penguin dictionary of biology, Research Council of Turkey, Penguin Books Ankara, Turkey Woynarovich, E and L. Horváth, 1980 – Bond, C.E., 1996 – Biology of Fishes, The Artificial Propagation of Saunders College Publishing, Warm-water Fish Species – A Orlando, Florida, 750p. manual for Extension, Edwards, D. 1989 – Training Course in FAO Fisheries Technical Papers Coldwater fish Culture, Technical No. 201, 183p. Cooperation Programme, Lectures 18 SMALL SCALE ARTIFICAL PROPAGATION OF TROUT

GLOSSARY orange. The machine can more easily distinguish this colour from the white unfertile eggs. Therefore, the efficiency of Anadromous fishes sorting machines will increase. Those fish species which migrate from Chromosome marine to freshwater waters for spawn- It is a thread-like structure found in all ing, like trout or salmon are anadro- living cells that carry genetic informa- mous fishes. tion in the form of genes. Animal pole Daydegree (Do) It is the more active, multiplying pole of It is used to express the length of incu- an egg cell. bation or developmental period of non- Artificial propagation or reproduction feeding larvae. It is the summed up of fish value of daily average temperature of It is a collective term and comprises a water. If the actual water temperature wide range of different techniques and is lower more, if it is higher less days technologies which aim to produce young are needed for the development of em- fish under controlled farm conditions. bryo or non-feeding larvae. Elements of artificial reproduction of fish Diadromous fishes may be: Those fish species which migrate for Stripping of wild males and females spawning from marine to freshwater wa- during spawning season. ters or vice versa are diadromous Rearing of broodfish (females and species. Fish like eel which migrate from males). freshwater to sea water are catadro- Synchronized, stimulated or induc ed mous, while species like trout or salmon spawning of females and males. which migrate from the sea to the fresh- Striping and fertilization of eggs through water to spawn are anadromous fishes. stimulated or induced ovulation. Diapause Incubation of embryo and non-feeding Suspended development of an organ- larvae (yolk-sack fry) under controlled ism. It may occur if environmental con- fish hatchery conditions. ditions change to unfavourable. Depending on the produced fish species DO practiced techniques may include only It is the abbreviation of dissolved oxy- some or all of the listed elements. gen in the water which ensures respira- BW tion of fish. The actual oxygen content It is the abbreviation of body weight. of water depends on some important Catadromous fishes physical and chemical characteristics of Those fish species which migrate for water.Water can dissolve only a certain spawning from freshwater to marine quantity of oxygen at a certain temper- water, like eel are catadromous fishes. ature. The possible maximum dissolved Changing the colour of fertilised eggs oxygen content of water (100 percent On fish farms where removing of unfer- saturation) depends on the actual water tile eggs is done with photo sensor temperature and the partial pressure of based machines, carote noids are add - oxygen in the atmosphere. Dissolved ed to the feed of females. Carote noids oxygen content changes slightly with change the colour of fertile eggs to dark the quality and quantity of other dissolved materials. Altitude also modifies the oxygen content of water. Dormant (resting) stage At this development stage eggs are ready for final maturation and ovulation. During this stage females are waiting for favourable environmental con ditions of spawning. When suitable conditions arrive this stage ends and final maturation and ovulation of eggs occur. References / Glossary 19

oC DO oC DO oC DO oC DO oC DO (mg/l) (mg/l) (mg/l) (mg/l) (mg/l)

1 13.92 6 12.21 11 10.83 16 9.75 21 8.82 2 13.52 7 11.91 12 10.61 17 9.55 22 8.67 3 13.20 8 11.62 13 10.38 18 9.35 23 8.41 4 12.88 9 11.33 14 10.15 19 9.16 24 8.36 5 12.52 10 10.10 15 9.96 20 9.00 25 8.22

Endocrine pituitary. GnRH/A is the abbreviation of Table 5: It is the collective name of glands which gonadotropin releasing hormone ana- Dissolved oxygen produce hormones or hormone* like logues which are artificially pro duced in content of fully products and secrete them directly into order to induce ovulation and sperma- saturated water the blood system. tion in a female or male fish. at different Fecundity Gonads temperatures Egg production capacity of a female fish. In bony fishes gonads, ovary and testis Fertilization are paired and in most forms there is no It is the act when the male reproductive connection between the reproductive product, in case of fish sperm enters and urinary systems (Bond, 1996). In into an egg and initiates the division of trout the two systems connect into one the cell. joint urogenital papilla where they empty. Follicle The gonads develop from the peri- It is a sheath, protective covering and toneum in which primitive egg cells can connective tissue around egg cells. Its be found. function is to protect and nurture de- Habitat veloping eggs, eventually become a It is the environment of an organism or double layer of eggs (Woynarovich and community, characterized by its physi- Horvath, 1980). cal or biotic properties (Allaby, 1994). Gametes Haploid They are mature haploid* female (ovu- A haploid cell is a germ cell which has an lated egg) or male (sperm) germ cells. unpaired, single set of chromosomes*. They are able to unite into zygote* with Hormone another reproductive cell of the oppo- It is produced by specialised glands in site sex. order to regulate action of organs such Genotype as gonads. It is the genetic constitution of living or- Hypophysis or pituitary ganisms. It is a very important endocrine gland Germinal disk under the brain. It produces different It is the location on the top of the yolk hormones, among others gonado tro - where an egg cell is fertilized and cell- pins which stimulate and control the division starts. activity of gonads. This gland of sexu- Globulins ally matured male and female pre- These are simple proteins soluble in served with alcohol or acetone are salt solutions. used for inducing ovulation or sperma- GnRH/A tion in female and male fish. Gonadotropin releasing hormones are Hypothalamus secreted by the hypothalamus when fish It is a region of the brain under the thal- receive a favourable environmental amus through which fish receive and stimuli for spawning through their re- pass sensory information. ceptors and brain. These hormones, as Lacustrine their name indicates stimulate the re- A fish species is lacustrine if it is adapt ed lease of gonadotropin hormones in the to lake habitat*. 20 SMALL SCALE ARTIFICAL PROPAGATION OF TROUT

Meiosis bation of eggs but then they abandon the It is a type of cell division that results in hatched larvae. They wash out or build daughter cells with half of the number nests where developing eggs are venti- of chromosomes as the parent cell. lated and guarded. European catfish and Mitosis pikeperch belong to this group of fish. Fe- It is a type of cell division that results in cundity of these fish is also high. Fish daughter cells which have the same species of active parental care produce number and kind of chromosomes as less eggs. As a compensation they take the parent cell. intensive care of the developing eggs, Neuro-endocrine process hatched larvae and even the fry. The It is the response of sexually matured most well known representatives of sub- fish to favourable environmental stimuli strate spawning and mouth breeder carried by the receptors to the brain. As groups of freshwater fishes are tilapias. a result the brain together with the en- Peristaltic docrine system executes the develop- It is constrictions and relaxations of ment and release of eggs and sperms. muscles of the intestine or other canal- The schematic sequence of information type organs. This is an unintentional is: 1) Favourable environmental condi- waive-like movement which pushes the tions → 2) Receptors → 3) Brain → 4) content of the canal forwards. Hypothalamus that acts through go- Phenotype nadotropin releasing hormones (GnRH) It is the observable characteristics of → 5) Pituitary that acts through go- interactions between genotype and en- nadotropin hormones (GtH) → 6) Go- vironment. nads → 7) Secondary and accessory Pituitary sex characteristics; reproductive behav- See at hypophysis. iour and activity (Woynarovich and Hor- Primary oocytes vath, 1980; Bond, 1996). They are egg cells which develop from Ovary primitive egg cells with normal mitosis*. It is the female reproductive organ Riverine which produces eggs. A fish species is riverine if it is adapt ed Ovulation to a river habitat*. It is the release of matured eggs from Saprolegnia the ovary. The fungi responsible for saprolegnia- Parental care sis are secondary pathogens which ap- Parental care of egg laying bony fishes pear and develop after handling or any may be indirect, direct and the combina- traumatic damage caused to the skin tion of these two. At indirect parental care of a fish. parents select the type of spawning Symptoms caused by Saprolegnia spp. are ground where released and fertilized greyish-white patches on the skin which eggs and hatched larvae can safely de- have a cotton wool-like appearance velop and feeding larvae and developing under the water. fry can find both food and shelter. A char- Stripping acteristic of these fish species is that their It is the act of removing ovulated eggs fecundity is very high. Their females pro- and milt from female and male fish. duce several hundred thousands of Testis eggs. This ensures the survival of suffi- It is the organ which produces sperm. cient offsprings required for the mainte- Vegetal pole nance of the species. Substrate Also called vegetative pole. It is the less spawning common carp, breams, pike active yolky pole of an egg cell. and river spawning Chinese and Indian Vitellogenesis major carp and South American Caras- It is a longer process before each re- sius species are typical members of this productive season when the yolk builds group of cultured freshwater fishes. into the eggs. There are freshwater fish species which Zygote perform active parental care during incu- It is the name of fertilized eggs The FAO Regional Office for Europe and Central Asia Benczur utca 34, H-1068 Budapest, Hungary