Rainbow trout : Salmo gairdnerii Brown trout: Salmo trutta fario Brook trout : Salvelinus fontinalisGrown in cold waters, In India- trouts were introduced into the cold watersof Jammu, HP and in peninsular India- Nilgiris and Munnar ( Kerala)
Reproductive Biology Sexual dimorphism Distinguished during the breeding season. Lower jaw of males changes into a hooked beak , in females a genital papilla is seen. During breeding season the coloration is brighter in males.-In rainbow trout, males have lateral iridescent bands and vivid stripes on sides-which increase in number.-- In brown trout the belly turns blackish , white stripes at the outer margin of anal fin-- Brook trout – anal fin become red in colour.-- If belly of ripe female is pressed gently, eggs flow out.- In males the milt oozes out, if white and creamy it is of good quality.
Age at First sexual maturityIn males – above 2 yearsFemales above 3 years Spawning seasonRainbow trouts spawn in Spring – Jan to May.Brown trout- Dec- JanRainbow- Feb and March FecundityVery low, 1500-2000 eggs per kg body weight. Trout HatcheryHas 4 units1. Brood stock unit2. Egg taking unit3. Incubation unit4. Larval rearing unit
1. Brood stock unit : Fish collected from natural open waters when they are swimming upstream for breeding OR farm reared troutsRequirements of raising a brood stock in hatchery-A. Optimum climatic conditions- Limits of temperature- 12-14deg C for brook and 10-20 for the other species. Rainfall should be moderate. Steep areas are to be avoided. Area with adequate limestone and other mineral deposits are desirable to ensure mineral rich waterB. Adequate water supply- water from a rheocrene spring ( water runnig down a valley through a slope) and limnocrene spring ( spring located in a depression) are ideal water sources.C. Good quality water- Turbidity-near to zero. D.O- 9ppm. pH- 7.9-8.4D. Feeding : Good quality artificial feed is given , meat balls of snowtrout and mirror carp in 1:1 proportion @ 1-2%body weight .
Sex ratio: Males give milt many times over , so they can be stocked at half or even one third the number of females. Milt from 2 males is sufficient to fertilise eggs from 2-4 females. Eggs and milt are stripped into a dry pan ,(Dry method) and after fertilization the pan is half filled with water. This is the dry method., preferred over wet method.1. The sperms remain in a viable condition for longer time if it is not mixed with water.2. If the eggs come in contact with water, it swells, micropyle closes.2. Egg Collection UnitProcedure for taking eggs1. Hand stripping – one man, two men method2. Hand stripping after incision3. Australian method4. Swedish methodFertilisation-• Mixed in dry method, then half filled with water. Fertilization takes place.• This mixture is set aside for the eggs to harden.• Fertilised eggs have a greenish tinge – called green eggs.
• Eggs are counted using volumetric/ gravimetric/displacement method• Unfertilised eggs turn white . Since this process is very slow, it is quickened by stirring the eggs with bare hand.3. Incubation Unit After water hardening and counting the eggs are transferred to a hatchery for incubation.Incubation devices1. Flat troughs and trays2. Vertical flow incubators3. Vibert Box4. Jar incubators1. Flat troughs and trays- Classical device. Many meshed trays are kept in troughs and eggs placed in trays made of perforated stainless steel /Al/Zinc/Plastic. Californian type- short troughs-0.5X0.2X0.25 m. Long trough- 2-3 m in length, 0.5 to0.8 m width and 0.2 to 0.35 m in depth. Many trays can be kept.
2. Vertical incubators : Space saving technique. Shelves hold the incubation trayswhich has an external basket which can hold water.Eggs containing trays are kept in this basket. Tray is covered with mesh lid.The whole device is made in plastic.Water that flows into the uppermost tray after filling it flows into the tray below,passes out through the lowermost tray.
3. Vibert System : Eggs kept in a cage called vibert box designed by Vibert (1975).Box made up of plastic, is transparent. Holes drilled in the walls, smaller than eggs size, big enough for fry to escape.Holds about 1000trout eggs. Bottom of stream should have pebbles of size of hens egg. Box immersed in river bed where there is swift current and clear water.Against the sides of the box, larger stones are kept, so that fry can escape into thewater. On the top of the box, smaller gravel is placed, to prevent predators andensuring complete darkness. The fry escape into the river.
4. Jar System: Each jar- cylindro- conical , narrow end fixed to a water inlet. A layer of gravel is kept at the narrow part of the jar which prevents the swift movement Of eggs , reducing injury. Jars of 70 L capacity are used, 4 lakh eggs can be incubated at a time.Development of eggsDuration of incubation is prolonged and depends on water temperature.4 stages :1. Green egg- Newly fertilized egg.2. Eyed egg – embryo develops eye , visible thru egg envelope3. Alevin or sac fry- Hatchling, with heavy yolk on the lower side of the belly. 1.5 to 1.8 cm long, 45 to 50 gms, more than 50 % wight is from yolk sac.They Lie at the bottom of the apparatus. 15-18 days required for yolk sac absorption.4. swim up fry- When 2/3 rds of the yolk sac absorbed, larva starts moving towards the water surface. Starts feeding.
Care of eggs during Incubation- Period from fertilisation to hatching.1. Continuous water flow : eggs should be bathed in F W always.2. Rate of flow- 0.2 to 0.3 litre/min/1000 eggs. Ensures adequate O2 content and removal of metabolic wastes. Water flow should not be intense Might cause injury to the egg.3. Water temperature should range between 1.5 and 14 Deg C. Brown trout – incubation period- 72-90 days transformation of Alevin to swim up fry- 32-40 days at 3- 7 Deg C. When temp is 7-11 deg C, Incubation period - 36-53 days Alevin to fry stage – 10-12 days4. Water should be free of silt particles, to prevent setttlement on eggs and risk of infection.5. Oxygen content – 6-8 ppm.6. Direct sunlight ,electric light – harmful to the developing embryos. Eggs must be kept in darkness.7. Dead eggs should be removed , prevent infections esp. Saprolegnia . Disinfection should be done one day after fertilisation or during the eyed egg stage.
General hygiene :1. Disinfectant to prevent fungal infection – Malachite green, acriflavin, Gentian Violet, Pot. Permanganate.2. Prophylactic measure to prevent fungal attack- eggs+ malachite green @ 5mg/L For 30 minutes. The crystals are uniformly dissolved in water. The solution is flushed away and fresh water is pumped in, without disturbing the eggs.3. Treatment continues till the alevins emerge.4. Rearing unit for fingerlings :The alevins are reared in the hatching trough after removing the hatching trays ORThe alevins with 3/4rth of yolk sac absorbed are released into rearing tanks.Stocking density – 10000 per sq. m,Feed residues, dead fry and faecal matter are siphoned out from the tank everyday. Artificial feed is given. with zooplankton.Rearing is done under illumination.Trout fingerlings reared in tanks of size 3 X 1 X 0.75 m ,stocking density @ 50-100 no.s swim up fry per sq.m.Grow to 8-12 cm at the end of 6 months of rearing.