Introduction Culture of trouts and salmons (Salmonidae) originated much later than carps. Greater scientific effort has been concentrated on these groups. Salmonid culture has a long history in Europe and N. America. The main interest of early salmonid culturists was hatchery production of young ones.
Contd.. The recent upsurge in the production and profitability of the Atlantic Salmon and trout in Sea-water cages in Norway and Scotland and its distribution to far-off markets around the world have served to demonstrate the potential of salmonid culture. The major constraint to expansion of salmonid culture is the availability of adequate quantities of water of the required quality.
Contd.. It has been suggested that a freshwater rainbow trout farm using surface water in a temperate climate should have available a supply of about 5l/s for every ton of fish produced. Water from spring, bore-wells of clean flowing streams have been used for culture. Spring water is considered essential for a trout hatchery and is recommended for use in rearing upto swimming stage.
Water quality requirements The most important are temperature and oxygen concentration. Temperature around ̊ C are considered optimal for the growth of rainbow trout. Slightly lower temperature is required for salmonids. Water for salmonid hatcheries usually has 100% oxygen saturation. A pH of 7-8 is preferable. The concentration of CO2 has to maintained below 10mg/l.
Stages of Culture - Trout Broodstock Spawning Egg incubation Fry culture Fingerling production Growout
Broodstock Females are 2 to 3 years old –Can be used for more than one year but may have decreased egg quality and quantity Males are 2 to 3 years old –Can be used several times in one spawning season but not for more than one year
Contd… The techniques of broodstock development, stripping, fertilization, incubation of eggs and larval rearing are very similar for rainbow and brown trouts. The natural methods of spawning, fertilization and incubation of eggs in redds on the stream beds are used for some salmons. Commercial trout farming in ponds originated in Denmark.
Contd.. The farms consists of earth ponds. Rectangular in shape, 30m x 10m with bottom sloping towards the outlet and a depth of 1m at the upper and 1.7m at the lower end. Capacity of such pond is about 1500kg rainbow trout. The most widely used system of trout culture is in raceways.
Contd… The stocking density depends on water temperature, but is around 4-5kg/m3 when water exchange is 2.5l/min per m3. Another system in use is tank culture. Tanks are 4-10m in diameter and 1.6m deep. Cage farming of trout is a rapidly expanding system and increasingly being used in both freshwater and saltwater environments.
Contd… A trout culturist may produce only eyed ova for shipment and sale to producers or may hatch. Many rear them to market size for sale to consumers either fresh or after processing. Monoculture and intensive systems are considered necessary in most situations to make the operation economically attractive.
Contd… In areas where climatic conditions are conducive, double cropping systems have been introduced.
Techniques of Propagation Stripping and fertilization: Brood fish are removed from brood or holding ponds/tanks. Dry method of fertilization without admixture of water is most commonly followed. Two to four females may be stripped at a time. Afterward the males are stripped and the milt poured over the eggs.
Contd.. Mixed well with a feather or spoon and allowed to stand for a minute or two. Slowly filled the bowl with water and allowed to stand for about 10 minutes. After successive changes of water to remove surplus milt, the eggs are transferred to a bigger container two/third full of water.
Contd.. Different types of incubators are used for hatching salmonid eggs but the best system is troughs and California baskets. Troughs are usually 40-50cm wide and 20cm deep convenient length is about 3-4m. The perforated bottom of the basket rests about 3cm above the bottom of the trough. The water flows from the top end of the trough, under the basket and passes up through the perforated base through the eggs and to next basket. Trough would need a continuous water flow of 500l/day for every eggs.