Rainbow trout Oncorhynchus mykiss

Rainbow trout is a Pacific-slope salmonid native from the Kuskokwim River in Alaska to the Otay River in California, introduced for farming and angling across the world, and occurring both as a resident freshwater form and as an anadromous sea-run form. FAO FishStat records 1,181,668 tonnes of farmed production in 2024. FishBase gives a maximum published length of 123 cm, a maximum weight of 25.9 kg and a maximum reported age of 11 years, with 700 to 4,000 eggs per spawning, and FishBase and Ontario's aquaculture service agree that males mature at about two years and females at about three. It is a cold-water fish: Ontario gives an optimum of 13 to 18 degrees C against a tolerable 0 to 24, and stock is grown in raceways and net pens with oxygen saturation held at 80 to 100 per cent, reaching market size in a little over a year and harvest at about two years old. Because trout are ectotherms, water temperature sets metabolic rate, drug elimination and therefore withdrawal periods: in yellow catfish the enrofloxacin withdrawal interval for muscle and skin lengthened from 61 days at 25 degrees C to 72 days at 15 degrees C. Bacterial cold-water disease, caused by Flavobacterium psychrophilum, is the industry's defining loss, and USDA ARS has bred and released a resistant line.