Rainbow trout

Quick facts

Adult size

50 cm, 800 g typical harvest weight

Days to harvest

270 to 540 days from fingerling

Lifespan (max)

up to 11 years

Diet

carnivore

Temperature class

cold-water

Difficulty

advanced

Water parameters

Temperature range

4–21°C (optimum 15°C)

pH

6.5 to 8

Hardness

5 to 20 dGH

Minimum tank

400 L per individual at harvest size

Feed and growth

Feed protein

45% target

Daily feed (warm water)

1.00% of body weight per day

Daily feed (cool water)

1.20% of body weight per day

Max stocking density

30 g per litre of system water

A 800g adult eats about 8.0 g of feed per day at optimum temperature. For a roster of 10 fish at adult size, that's around 80 g of feed daily.

Legality

Aquaculture and possession rules vary by jurisdiction and change over time. This table reflects regulations as of the verified date on each row. Verify with your local fisheries or wildlife authority before stocking.

Jurisdictions not listed here default to "check local regulations". A non-listing is not a green light; rules in your specific county or municipality may apply.

Habitat and origin

Native to Pacific drainages of North America, from Alaska through California and inland to the Rocky Mountains. Introduced worldwide for sport fishing and aquaculture; now farmed commercially in Chile, Norway, Iran, Turkey, Italy, and across Europe. The species (Oncorhynchus mykiss) requires cold, well-oxygenated water: optimal temperature is 12–16°C, with an upper lethal limit around 24–25°C. Wild populations live in clear, fast-flowing streams and cold lakes. Rainbow trout are the premier cold-water aquaculture species globally, with well-established genetics, feed formulations, and disease management protocols. Growth is fast in ideal conditions, reaching 250–400 g in 12-15 months on high-quality feed. The flesh is pink to orange (depending on diet) with a mild, clean flavor. Market demand is consistently strong.

Climate and outdoor ponds

Climate classification

cold-water (cool water required, dies in heat)

Outdoor pond zones (USDA)

3 to 7 (winter low around -40°C or warmer)

Heating in a temperate climate

Not required (handles seasonal cool periods)

Cooling in a temperate climate

Required if your summer water temperatures exceed the upper tolerance

Zone bounds reflect year-round outdoor pond viability with no active heating. Anywhere outside the bounded zone, the species can still be kept in an indoor heated tank or a seasonally-managed system. Verify your specific microclimate, as a sheltered yard zone can run a half-zone warmer than the regional rating.

Care notes

The cold-water counterpart to tilapia in aquaponics. Trout systems operate at 10–18°C, which means they're viable in temperate climates without heating costs but often need active cooling in summer. Above 21°C, trout stress visibly (gasping at the surface, loss of appetite); above 24°C they die within hours. A chiller or cold-water supply is non-negotiable in climates where water temperatures exceed 20°C during summer. Dissolved oxygen must stay above 6 mg/L at all times; trout die rapidly below 4 mg/L. This oxygen requirement drives the system design: vigorous aeration using fine-bubble diffusers, venturi injectors, or cascade/splash bars on the tank return are standard. FCR is excellent at 1.1-1.5 on high-quality trout pellet (40-45% protein), making them among the most efficient feed converters in aquaculture. Stocking density in aquaponics: 15-30 g/L depending on oxygenation capacity. Trout are more sensitive to ammonia than tilapia or catfish; keep total ammonia nitrogen below 1 mg/L and un-ionized ammonia below 0.02 mg/L. Disease management is more demanding than warm-water species: bacterial kidney disease (BKD), enteric redmouth disease (Yersinia ruckeri), and Saprolegnia fungal infections are the main concerns. Fingerlings are available from trout hatcheries (many state-run programs sell surplus stock). Legal in most jurisdictions. The premium retail price ($8-15/kg) offsets the higher operating costs of cold-water systems.

Further reading

• Fish for aquaponics: tilapia vs everything else