Rainbow Trout Farming: A Production Guide
How rainbow trout (Oncorhynchus mykiss) is farmed: cold-water requirements, raceway and tank culture, high-protein feed and FCR, hatchery and egg supply, growth to market and main diseases.
Overview
Rainbow trout (Oncorhynchus mykiss) is a salmonid native to the Pacific basin of North America and eastern Asia, and it is the leading farmed cold-water fish. It is grown worldwide for the table; global farmed production has been on the order of 600,000 to 800,000 tonnes a year, with Chile among the largest producers. Trout farming depends on a reliable supply of cold, clean, well-oxygenated water.
Water requirements
As a cold-water species, rainbow trout grows over a range of roughly 10 to 20 °C, with feed efficiency and performance generally best near about 15 °C; it tolerates 0 to around 25 °C but stops thriving in warm water. It needs high dissolved oxygen and clean, flowing water, which is why production is concentrated where cool springs or rivers are available.
Culture systems
- Flow-through raceways: the classic system, with continuous cold water passing through linear concrete channels.
- Earthen ponds: used where cold spring or stream water is available.
- Cages and net pens: in cold lakes and, for large trout, in the sea (notably in Chile and Norway).
- Recirculating aquaculture systems (RAS): for intensive, controlled production with water reuse.
Feeding and growth
Rainbow trout is a carnivore requiring a high-protein diet, historically based on fishmeal and fish oil and increasingly supplemented with alternative protein sources. It converts feed efficiently; reported feed conversion ratios are roughly in the 1 to 2 range depending on diet and management. FAO production figures cite yields on the order of 100 to 200 tonnes per hectare over a 14 to 15 month cycle in well-supplied systems. Fish are grown to a portion size or to larger sizes for further processing.
Hatchery and seed supply
Rainbow trout spawn when water reaches about 6 to 7 °C. In the hatchery, eggs and milt are stripped from broodstock and fertilized by the dry method, and the fertilized eggs are incubated in trays or jars. The robust eyed-egg stage can be shipped, supporting an international trade in trout eggs. Many farms stock triploid and all-female fish, which are sterile or do not mature early, to avoid the loss of flesh quality that comes with sexual maturation.
Main diseases
Rainbow trout is susceptible to several important diseases, including the viral diseases infectious haematopoietic necrosis (IHN) and infectious pancreatic necrosis (IPN), the parasitic whirling disease (Myxobolus cerebralis), bacterial kidney disease (BKD) and enteric redmouth disease (yersiniosis, caused by Yersinia ruckeri), and fungal saprolegniosis on eggs and stressed fish. Good cold-water quality, low stress and biosecurity are the main controls, with vaccines available for some diseases.