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Rainbow Trout (Oncorhynchus mykiss)

Читати українською(переклад на редакторській перевірці)

FishSalmonidIntroduced Worldwide

A rainbow trout (Oncorhynchus mykiss) swimming above a stony riverbed, showing the pink flank stripe and dark spotting.

A rainbow trout (Oncorhynchus mykiss) underwater.

Image: Liquid Art, CC BY-SA 4.0, via Wikimedia Commons.

Overview

The rainbow trout (Oncorhynchus mykiss) is a salmonid native to the Pacific drainages of North America and northeastern Asia, named for the broad pink or reddish stripe along its flank and the fine black spotting scattered across its body and fins.

Despite being called a trout, it belongs to the Pacific salmon genus Oncorhynchus rather than to the genus containing the brown trout — a detail that reflects its true relationships.

The species has two life histories in one. Fish that stay in fresh water are 'rainbow trout'; those that migrate to sea and return to spawn are called steelhead, and grow larger and more silvery. They are the same species, differing in life history rather than in identity.

Habitat & Range

Rainbow trout are native to cool, clean, well-oxygenated fresh water on the Pacific side of North America and in parts of northeastern Asia, and steelhead populations use the north Pacific. Through deliberate introduction for angling and aquaculture the species now occurs on every continent except Antarctica, in rivers, streams, lakes and reservoirs where temperatures stay cool enough.

Diet

Rainbow trout are opportunistic carnivores. Diet varies with size and habitat: aquatic insect larvae, adult insects taken at the surface, crustaceans, molluscs, fish eggs and smaller fish. Larger individuals take proportionally more fish. Sea-run steelhead feed heavily in the ocean on fish and crustaceans, which is why they grow so much larger.

Behavior

Rainbow trout spawn in spring in gravel-bottomed streams, where the female excavates a depression called a redd, deposits eggs, and covers them with gravel. Unlike most Pacific salmon, which die after spawning, rainbow trout and steelhead can survive to spawn again. Stream-resident fish hold feeding positions in current where drifting food passes, defending those positions from other trout.

Human Interaction & Conservation

Rainbow trout are one of the most widely introduced fish in the world, moved deliberately for sport fishing and farmed extensively in aquaculture. That success has costs: introduced populations can outcompete or hybridise with native fish and alter stream communities, and rainbow trout are treated as an invasive species in a number of countries. In parts of their native range certain steelhead populations are of serious conservation concern even while the species globally is abundant. This profile is educational and offers no fishing or aquaculture guidance. Verify current status at the IUCN Red List and NOAA Fisheries.

Sourced facts

Each value below is traced to the specific reference that states it. Open a row's evidence to see the source, where to look in it, and how firmly it supports the value. Sources checked 2026-10-09.

Sourced facts about the Rainbow Trout, with the reference supporting each
Geographic rangeNative to the Pacific coast of North America, from Alaska to the California–Mexico border; introduced throughout the US and to every continent except Antarctica for game fishing.ADW gives only the North American native range and calls it the only native range; the profile also describes a native population in northeast Asia, which this source does not cover. Introductions as ADW lists them.
Matches source · Animal Diversity Web — how we know
Animal Diversity Web — University of Michigan Museum of Zoology
Where
Geographic Range
Checked by FaunaHub
2026-10-09
Limits
A peer-edited account written largely by students under faculty review. Figures are compiled from the literature rather than from a single study, and some are regional.
HabitatTemperate fresh, brackish or marine waters. In fresh water it prefers cool water, tolerating up to 24°C (native summer water around 12°C). Elevation 0 to 3000 m; depth 10 to 200 m.Steelhead spawn and develop in freshwater mountain streams, then spend their adult life in the ocean. Spawning needs gravel beds, so the fish are sensitive to sedimentation and channel scouring. Productive streams mix riffles, pools and overhanging vegetation, and juveniles need cover and slow water. ADW does not say which form the elevation and depth figures describe.
Matches source · Animal Diversity Web — how we know
Animal Diversity Web — University of Michigan Museum of Zoology
Where
Habitat
Checked by FaunaHub
2026-10-09
Limits
A peer-edited account written largely by students under faculty review. Figures are compiled from the literature rather than from a single study, and some are regional.
DietInsectivorous and piscivorous; mainly drifting invertebrate larvae in mid-water. Young eat insect larvae, crustaceans, other aquatic invertebrates and algae. Residents eat more fish than steelhead.ADW says drift-feeding saves the energy that foraging in the substrate would cost. ADW calls the resident and steelhead forms 'both species', though elsewhere it treats them as two forms of one species.
Matches source · Animal Diversity Web — how we know
Animal Diversity Web — University of Michigan Museum of Zoology
Where
Food Habits
Checked by FaunaHub
2026-10-09
Limits
A peer-edited account written largely by students under faculty review. Figures are compiled from the literature rather than from a single study, and some are regional.
Body sizeUp to 120 cm long; males are larger.ADW's maximum figure; the length measure is not stated.
Matches source · Animal Diversity Web — how we know
Animal Diversity Web — University of Michigan Museum of Zoology
Where
Physical Description
Checked by FaunaHub
2026-10-09
Limits
A peer-edited account written largely by students under faculty review. Figures are compiled from the literature rather than from a single study, and some are regional.
Body massAverage 4 kg; maximum 25.4 kg; males are larger.Data-field figures for the species as a whole: an average and an upper ('high') value. ADW gives no sex-specific masses and does not separate steelhead from resident fish.
Matches source · Animal Diversity Web — how we know
Animal Diversity Web — University of Michigan Museum of Zoology
Where
Physical Description
Checked by FaunaHub
2026-10-09
Limits
A peer-edited account written largely by students under faculty review. Figures are compiled from the literature rather than from a single study, and some are regional.
LifespanWild: typically 6 to 8 years, possibly up to 11 years.Wild figures only; ADW gives no captive lifespan and does not separate steelhead from resident fish.
Matches source · Animal Diversity Web — how we know
Animal Diversity Web — University of Michigan Museum of Zoology
Where
Lifespan/Longevity
Checked by FaunaHub
2026-10-09
Limits
A peer-edited account written largely by students under faculty review. Figures are compiled from the literature rather than from a single study, and some are regional.
Social structureSolitary: young leave the juvenile group after hatching. Resident fish keep small territories, and a size hierarchy gives the largest trout the best habitat.ADW's Key Behaviors tags are solitary, territorial and dominance hierarchies. Fry become hostile to each other once they emerge from the gravel. The mating system is polygynous: male steelhead often breed with several females.
Matches source · Animal Diversity Web — how we know
Animal Diversity Web — University of Michigan Museum of Zoology
Where
Behavior; Communication and Perception
Checked by FaunaHub
2026-10-09
Limits
A peer-edited account written largely by students under faculty review. Figures are compiled from the literature rather than from a single study, and some are regional.
Distinguishing traitsStreamlined; 8 to 12 anal-fin spines; no teeth at the tongue base (unlike close relative O. clarkii); pinkish red stripe along the upper-middle body; most have black spots above the lateral line.ADW says appearance varies widely with sex, age and habitat. Resident fish and spawning steelhead are lighter with stronger pink stripes, while ocean-going steelhead are darker and silvery. Resident fish are spotted more heavily, well below the lateral line, and juveniles have parr marks.
Matches source · Animal Diversity Web — how we know
Animal Diversity Web — University of Michigan Museum of Zoology
Where
Physical Description
Checked by FaunaHub
2026-10-09
Limits
A peer-edited account written largely by students under faculty review. Figures are compiled from the literature rather than from a single study, and some are regional.
Conservation statusLeast Concern (LC), global assessment, 2024
Matches source · IUCN Red List of Threatened Species — how we know
IUCN Red List of Threatened Species
Checked by FaunaHub
2026-10-09
Limits
Read from the Red List export IUCN publishes to GBIF; iucnredlist.org itself does not answer automated reads. Categories are reassessed over time.

Not stated here, and why

Activity pattern— no source accepted yet
The ADW account states no activity pattern. It gives a spawning season (March to July, from January for California winter steelhead) and describes steelhead spawning migrations, but no daily (diurnal or nocturnal) or seasonal activity pattern.

References for the facts above

  • UniversityAnimal Diversity Web — University of Michigan Museum of ZoologySupports: Range, habitat, diet, body size and mass, lifespan, activity and social structure, as the account states them. Retrieved 2026-10-09.Limitations: A peer-edited account written largely by students under faculty review. Figures are compiled from the literature rather than from a single study, and some are regional.
  • ReferenceIUCN Red List of Threatened SpeciesSupports: The global Red List category and the year of the assessment. Retrieved 2026-10-09.Limitations: Read from the Red List export IUCN publishes to GBIF; iucnredlist.org itself does not answer automated reads. Categories are reassessed over time.

Frequently Asked Questions — Rainbow Trout

What is the difference between a rainbow trout and a steelhead?
Life history, not species. Both are Oncorhynchus mykiss. Fish that spend their lives in fresh water are called rainbow trout; those that migrate to the sea, feed there and return to fresh water to spawn are called steelhead, and they grow larger and become more silvery.
Is a rainbow trout a salmon?
Genetically it sits with the Pacific salmon. Rainbow trout belong to the genus Oncorhynchus, which contains the Pacific salmon species, rather than to Salmo, the genus of the brown trout and Atlantic salmon. Unlike most Pacific salmon, though, it does not necessarily die after spawning.
Where are rainbow trout originally from?
The Pacific drainages of North America and parts of northeastern Asia. Their presence across every continent except Antarctica is the result of deliberate introduction for angling and aquaculture, not natural range expansion.
Are rainbow trout invasive?
In many places, yes. Because they have been introduced so widely for sport and farming, rainbow trout can compete with or displace native fish and change stream communities, and several countries treat them as invasive. Within their native range, by contrast, some steelhead populations are themselves of conservation concern.

Sources and further reading

Authoritative wildlife references used for general educational context. Conservation status should always be verified against current IUCN Red List data. External links open in a new tab.