Rainbow trout is carnivorous exotic fish which grows well in cool & clean flowing water. It is supposed to be originated from California of North America & supposed to be diversified to Europe & Asia in the 19th century. As it is carnivorous fish, higher animal protein containing feed is to be supplied. This fish contains human preferred smell, omega-3 fatty acid & lack small intermuscular Y bones which make easier & protective consumption of fish. It has wide body, length four times the height of fish, small head, small scales with rainbow colored line along the body length ae its beautiful distinguishing features.
History in Nepal:
Among the fish species suitable for cultivation in cold water & higher altitude, rainbow trout is one of the best. The higher hilly region of Nepal contains abundant source of cold water which makes greater possibility of farming of rainbow trout in Nepal. Japan government aided in first starting commercial cultivation of this species through different researches carried out in Nepal. At present it is in the phase of extension to mid hills & Himalayan region of country.
For the commercial cultivation of this fish, water, land, transport, electricity & market are basic requirements. For the selection of suitable site, consult with the technician if available.
For the successful rainbow trout fish farming, continuously running cool & clean water supply is necessary. The temperature of water must be within range of 0 to 25 degree Celsius. The optimum temperature for this fish growth & development is between 14-18 degree Celsius. For commercial cultivation, temperature range is 14-20 & for the fry production 8-14 degree Celsius is necessary. Dissolved oxygen in the water is to be greater than 6mg/liter of water along with pH of water between 6.5-8.
Transport & market:
Rainbow trout fish is cultivated feeding with artificial feed in cold water which is expensive than other fish species. So, during fry transportation, fish feed transportation & storage which are extremely sensitive must be handled with proper care. So, the good transportation facility is necessary with better & scheduled marketing scenario is essential. Any sort of loss must be prevented & at most concern, the market should be nearby to the farm for higher profitability.
Fish feed of trout fish is expensive & degrades earlier than other fish species. So, storage of fish feed must do with great care. Refrigerator can be used to store the feed to avoid the disease attack in fish through feed.
Security & care:
Site is to be selected nearer to the society or to the house. Protection from illegal acts like poisoning the water, stealing fishes must be ensured for overcoming extra economic loss. Make easier supply of inputs to ensure proper functioning of farm.
Artificially feeding food to the fish is defined as fish feed. Rainbow trout fish feeds on naturally occurring insects, crustaceans, & small fish. As this fish is carnivorous in feeding behavior, animal protein rich feed is necessary for feeding them. It requires feed containing greater than 35% crude protein which can be prepared from Jhinge fish, soybean or soybean cake, mustard cake or mustard cake powder, rice bran, wheat flour by making crumble or balls according to fish size & mouth.
Proper storage of the artificially prepared feed is primary for ensuring zero feed loss. Fungus attack will be faster & higher if no good arrangement of feed is ensured. This will lead to degradation of feed, attack of diseases in fish & malnutrition may occur in fish feeding such feed.
Feed amount & time:
Feed constitutes about 70% of total cost of production of trout fish. The physical growth of fish is determined by feed & thus the feed amount must be equal to 2 to 10% of body weight of fish, water quality & fish size & growth status. Small fish is feed for 8 times whereas only 2 feeding is done for large sized fish in a day.
Farm Layout & design:
The pond for rainbow trout farming is raceway channel. Pre-construction survey is essential of the site selected to avoid future problems associated with farming. Fry production ponds, breeding ponds, cultivation ponds, feed storage house, office, research raceways, roads & walkways must be designed properly so as to ensure future extension of the farm. Water entry, exit, good drainage, pond size, farm perimeter, fencing are essential part to be done before constructing the raceways ponds & infrastructures.
Better consult the technician for the layout & design.
Diseases & parasites:
Trout farming is extremely sensitive where small changes in sound environment may lead to degradation of environment. High density, feed quality, feed amount, raceway construction, & management are within the sensitive field of farming. Changes in these requirements cause disease & parasite attack through water & feed.
Consultant with technician is necessary for treatment in case of any disease attack in fish.