Animal
Rainbow trout
The rainbow trout is a fish with a pink stripe on its side. It lives in cool rivers and lakes. Some swim out to the sea.
The rainbow trout gets its name from the pink-red band along each side. It comes from the cool rivers and lakes of western North America and far eastern Russia. Some rainbows stay in fresh water all their lives, while others, called steelhead, swim out to the ocean and come back to spawn.
Oncorhynchus mykiss is a Pacific salmonid with two life histories: resident rainbow trout that stay in fresh water and anadromous steelhead that feed at sea. Native to the North Pacific rim, it has been stocked widely around the world for sport fishing and farmed for food. The IUCN lists it as Least Concern, while several steelhead populations are protected in the United States.
Photo: USFWS Mountain-Prairie, public domain, via Wikimedia Commons
Meet the rainbow trout
The rainbow trout is a sleek, speckled fish.
A pink stripe runs along its side, like a little rainbow. Tiny black spots cover its back and tail. It lives in cool, clean water.
The rainbow trout is named for the reddish-pink band that runs along each side. That stripe can be faint or bright, depending on where the fish lives. Its back is blue-green to olive, its lower sides are silver, and small black spots cover its back, upper fins and tail.
Rainbow trout are close relatives of salmon. Some spend their whole lives in rivers and lakes. Others, called steelhead, swim out to the ocean, grow bigger and come back to fresh water to spawn. Scientists can only tell for sure by looking at a fish's scales or ear bones.
Oncorhynchus mykiss belongs to the Pacific salmon genus. Body shape and color vary with habitat, age, sex and maturity, but the Alaska Department of Fish and Game describes a blue-green to olive back, a reddish-pink lateral band, silver lower sides and small black spots above the lateral line and on the upper fins and tail. Positive identification uses 8 to 12 anal fin rays, a mouth that does not reach past the back of the eye, and no teeth at the base of the tongue.
The species has two life histories. Resident rainbow trout stay in fresh water; steelhead are anadromous. The US Fish and Wildlife Service notes that the two forms can only be confirmed by scale or otolith chemistry, and that offspring of either form may take the other path.
Quick facts
- Group
- Fish
- Length
- 0.46 to 0.61 m
- Lifespan in the wild
- up to 11 years
Where it lives
Wild rainbow trout come from cool rivers near the Pacific Ocean.
They live in Canada, the United States, Mexico and far eastern Russia. People have taken them to many other countries too.
Wild rainbow trout are native to streams along the Pacific coast of North America, from Alaska's Kuskokwim River south into northern Baja California in Mexico. They also live in parts of Alberta and British Columbia in Canada, and across the Pacific on Russia's Kamchatka Peninsula.
Rainbow trout like cool, clear water with plenty of oxygen. People have released them for fishing in many other places, in North America and around the world, from New Zealand to the mountains of South America and Europe.
The IUCN gives the native range as Pacific coast streams of North America from the Kuskokwim River drainage, Alaska, to northern Baja California, plus the upper Mackenzie drainage in Alberta and British Columbia, inland basins of southern Oregon and the Commander Islands. In Russia it lives on both coasts of Kamchatka, with a relict population on Bol'shoy Shantar Island in the Sea of Okhotsk. At sea, steelhead range across the North Pacific north of 40° N. Native countries: Canada, Mexico, Russia and the United States.
It does best in cool, clear, well-oxygenated water (at least 7 ppm dissolved oxygen). Introductions began in the late 1800s; FishBase records established populations from New Zealand (1877) and Australia (1894) to Chile (1905), Peru (1927) and Bolivia (1942), and across Europe. The map shows native countries and a sample of established introductions separately.
Continents
Its habitat
Where can you find this animal?
- Brought here by people · Countries and seas named by a scientific source
- Lives here naturally · Countries and seas named by a scientific source
- Sightings recorded · Records of wild sightings (GBIF)
Brought here by people · Countries and seas named by a scientific source
A sample of countries where FishBase lists introduced rainbow trout as established, from New Zealand (1877) to the Dominican Republic (1985). Rainbows have been stocked in many more places, including much of the United States and Canada outside the native range.
Places: New Zealand, Australia, Chile, Peru, Bolivia, Italy, Switzerland, Denmark and 6 more places.
Source: https://www.fishbase.se/Introductions/IntroductionsList.php?ID=239&GenusName=Onc · checked October 2026
Lives here naturally · Countries and seas named by a scientific source
Pacific-coast streams of North America from Alaska's Kuskokwim River to northern Baja California, the upper Mackenzie drainage in Alberta and British Columbia, and Russia's Kamchatka Peninsula; steelhead roam the North Pacific north of 40° N. Each country is shaded, but wild native trout live only in these western drainages.
Places: United States, Canada, Mexico, Russia and Pacific Ocean.
Source: iucn-red-list · checked October 2026
Sightings recorded · Records of wild sightings (GBIF)
Counts of GBIF records of wild observations (human and machine) and preserved specimens. Records include introduced populations, vagrants, escaped or released animals and misidentifications, so a country with records is not necessarily part of the native range.
Wild sightings have been recorded in United States, Canada, France, New Zealand, Sweden, UK, Switzerland, Germany and 71 more places.
Source: gbif · checked October 2026
Range maps show where scientists say an animal lives, often country by country. An animal may live in only part of a country shown, and sightings records can include animals that wandered far from home.
What it eats
Young trout eat tiny water bugs and little shrimp-like animals.
Big trout eat other fish and fish eggs. Some even catch a mouse!
Young rainbow trout gather along stream edges and eat small crustaceans, aquatic insects and their larvae, and bits of plants. After two or three years they move into bigger rivers and lakes and start eating more fish.
In Alaska, big rainbows also feed on salmon eggs and on the bodies of salmon that have died after spawning. As steelhead grow up, they add fish eggs, crustaceans, mollusks and small fish to their diet, and trout have even been known to eat small mammals such as mice.
Fry emerge from the gravel and school along protected margins, eating crustaceans, plant material and aquatic insects and their larvae. After two or three years in similar habitat they move to larger water and shift toward fish, salmon carcasses and eggs, and occasionally small mammals (Alaska Department of Fish and Game).
The link with salmon matters: in Alaska, resident rainbows that live in or migrate to large lakes with sockeye salmon runs generally grow faster and larger than those that stay in streams year-round. The USFWS describes steelhead moving from zooplankton when young to fish eggs, crustaceans, mollusks, small fish and even mice as they mature.
Did you know?
Trout babies can grow up to be sea travelers or river stay-at-homes.
Two steelhead parents can have young that stay in fresh water, and two stay-at-home rainbows can have young that go to sea.
Resident and anadromous O. mykiss can interbreed, and females may produce offspring with the opposite life history, so the two forms may function as a single population.
A speckled, streamlined body
A rainbow trout has a smooth, long body for swimming fast.
It has a pink stripe, a silver belly and lots of little black spots. Its tail has spots too.
Rainbow trout have the streamlined shape of salmon and trout, built for swimming in fast water. Some are slim and some are thick. The pink stripe is brightest in fish that live in rivers and streams, which also have the most spots.
Steelhead that go to sea are usually more silver and grow larger than rainbows that stay in fresh water. Fish that are ready to spawn turn darker overall.
The body follows the fusiform salmonid plan, though it ranges from slender to thick. River and stream residents usually show the most intense pink stripe and the heaviest spotting, followed by lake and lake-stream fish; in some places the black spots of adults extend below the lateral line and can cover the lower sides. Spawning fish are generally darker.
Steelhead are typically more silvery and larger than resident fish; the USFWS reports that steelhead can jump 11 feet into the air when climbing waterfalls and accelerate from zero to 25 miles per hour in one second.
Growing up
A mother trout digs a nest in the gravel with her tail.
She lays eggs there and covers them up. Tiny fry hatch and hide near the river's edge. Trout can lay eggs again and again.
Between late March and early July, female rainbow trout use their tails to dig nests called redds in shallow gravel riffles. Each nest is about 10 to 30 centimeters deep, and the female lays 200 to 8,000 eggs, which a male fertilizes before she covers them with gravel.
The eggs hatch after a few weeks to four months, depending on water temperature, and a few weeks later the tiny fry wiggle out of the gravel. Most Alaska rainbows become adults at 6 or 7 years old. Unlike Chinook salmon, rainbows and steelhead do not have to die after spawning: they can spawn more than once.
Spawning in Alaska runs from late March through early July. The female cuts a redd 4 to 12 inches deep and 10 to 15 inches across, depositing 200 to 8,000 eggs; incubation takes a few weeks to four months depending on temperature, and fry emerge a few weeks after hatching. Maturity varies with density, productivity and genetics: spawners as young as 3 (males) and 5 (females) occur, but most mature at 6 to 7, and fish up to age 11 have been seen spawning.
Unlike most Pacific salmon, O. mykiss is iteroparous. Steelhead return to the sea between spawnings and come back to their natal stream each time, some in consecutive years and some skipping a year. Juveniles may leave for the ocean within months of hatching or stay up to a year in fresh water (USFWS).
Stay-at-home trout and ocean travelers
Some rainbow trout stay in their river all their lives.
Others swim far out to sea and come back. These travelers are called steelhead. They can leap up waterfalls!
Rainbow trout make two very different choices. Resident rainbows stay in fresh water, and in Alaska some move between lakes and streams. Steelhead swim out to the ocean to feed, then find their way back to the stream where they hatched.
Steelhead are strong athletes. They have been seen leaping 11 feet (more than 3 meters) into the air to climb waterfalls. Amazingly, two steelhead parents can have young that stay in fresh water, and two stay-at-home rainbows can have young that go to sea.
Life history in O. mykiss is flexible rather than fixed. The USFWS notes that the offspring of two steelhead may become resident rainbows, and the offspring of two residents may become anadromous; the IUCN says the two forms may form one interbreeding population, which complicates conservation because protecting steelhead may require protecting resident fish too.
Steelhead migration patterns are not fully understood. Some fish spend several years at sea, others only a few months, and seasonal shifts in their ocean distribution track water temperature. In Kamchatka, spawning migrations begin in spring as snow and ice melt and water rises above 3°C.
Did you know?
In Alaska, some big trout follow salmon and eat their eggs.
In Alaska, large rainbow trout feed on salmon eggs and on salmon that have died after spawning.
Alaska rainbows living in or migrating to large lakes with sockeye salmon runs generally grow faster and larger than stream-resident fish (Alaska Department of Fish and Game).
Wild rainbows, hatcheries and protection
There are lots of rainbow trout in the world.
But some wild groups, especially steelhead, need help. People take care of rivers and protect these fish.
The IUCN lists the rainbow trout as Least Concern because it is so widespread and numerous. But some wild groups are in trouble. In the United States, NOAA Fisheries protects one steelhead group as endangered and ten as threatened. Dams, blocked culverts and damaged streams are major problems.
Hatcheries raise rainbow trout to stock lakes and rivers for fishing and for food. Released trout can also cause problems: they can mix with rarer native trout, such as cutthroat trout, and hatchery stocking has spread whirling disease to open waters in about 20 US states.
The IUCN assessed O. mykiss as Least Concern on 28 July 2020 (published 2024), with a stable overall trend, but warns that species-level status masks many significant declines driven by dams, sedimentation, overfishing, pollution and invasive species. In Kamchatka numbers have recently fallen sharply because of poaching, even though there is no official fishery for the species there. As of NOAA Fisheries' page updated in September 2026, one steelhead distinct population segment (Southern California) is endangered under the US Endangered Species Act and ten are threatened.
The species is farmed and stocked worldwide, and introductions have costs. The US Geological Survey records hybridization with cutthroat, golden, Gila and Apache trout, and the spread of whirling disease through hatchery stocking into about 20 states; in Montana's Madison River the disease cut the rainbow population by 90 percent. Keeping rainbows out of native-trout waters is a management priority, according to the IUCN.
IUCN Red List
How is the rainbow trout doing in the wild?
- Least Concern (this animal)
- Near Threatened
- Vulnerable
- Endangered
- Critically Endangered
- Extinct in the Wild
- Extinct
Least Concern
Not at risk of disappearing from the wild right now.
Amazing facts
-
Steelhead trout can leap up waterfalls.
Steelhead have been seen jumping 11 feet into the air to get up waterfalls on their way home.
The US Fish and Wildlife Service reports steelhead leaping 11 feet when climbing waterfalls and accelerating to 25 miles per hour in one second.
-
Trout babies can grow up to be sea travelers or river stay-at-homes.
Two steelhead parents can have young that stay in fresh water, and two stay-at-home rainbows can have young that go to sea.
Resident and anadromous O. mykiss can interbreed, and females may produce offspring with the opposite life history, so the two forms may function as a single population.
-
In Alaska, some big trout follow salmon and eat their eggs.
In Alaska, large rainbow trout feed on salmon eggs and on salmon that have died after spawning.
Alaska rainbows living in or migrating to large lakes with sockeye salmon runs generally grow faster and larger than stream-resident fish (Alaska Department of Fish and Game).
Words to know
- steelhead
- a rainbow trout that swims to the sea and comes back to fresh water to spawn
- redd
- a nest a trout digs in river gravel for its eggs
- fry
- a very young fish that has just come out of the gravel
- hatchery
- a place where people raise young fish
- introduced
- brought by people to a place where it did not live before
- iteroparous
- able to have young more than once in a lifetime
Discovery challenge
-
What gives the rainbow trout its name?
Which feature gives the rainbow trout its name?
Which body feature is the rainbow trout named for?
- A pink stripe along its side
- Its rainbow-colored tail
- It lives under rainbows
Show the answer
A pink stripe along its side
A pink stripe runs along each side, like a little rainbow.
A reddish-pink band runs along each side. It can be faint or bright.
The reddish-pink lateral band, most intense in river and stream residents, gives the species its common name.
-
What do we call a rainbow trout that swims to the sea?
What is a rainbow trout that migrates to the ocean called?
What is the name for the anadromous form of Oncorhynchus mykiss?
- A goldfish
- A steelhead
- A seahorse
Show the answer
A steelhead
Rainbow trout that go to the sea are called steelhead.
Steelhead are rainbow trout that swim to the ocean, grow bigger and come back to spawn.
Steelhead are anadromous O. mykiss; residents stay in fresh water, and the two forms can interbreed.
-
Can a rainbow trout lay eggs more than once?
Unlike a Chinook salmon, can a rainbow trout spawn again after laying eggs?
Unlike most Pacific salmon, can O. mykiss spawn in more than one season?
- Yes, it can spawn more than once
- No, it always dies after spawning
- It never lays eggs
Show the answer
Yes, it can spawn more than once
Yes! Rainbow trout can lay eggs again in later years.
Chinook salmon die after spawning, but rainbow trout and steelhead can spawn more than once.
O. mykiss is iteroparous; steelhead return to sea between spawnings, some spawning in consecutive years.
-
Where do wild rainbow trout first come from?
Where is the rainbow trout's native home?
Which region is the native range of O. mykiss?
- Africa's deserts
- Rivers around the North Pacific
- The Amazon rainforest
Show the answer
Rivers around the North Pacific
Wild rainbows come from rivers near the Pacific Ocean in North America and Russia.
They are native to western North America, from Alaska to Mexico, and to Russia's Kamchatka Peninsula.
Native countries are Canada, Mexico, Russia and the United States; elsewhere the species was introduced by people.
Places where you might see it
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Watch
Country
United States
The United States is a large country in North America made of 50 states, from icy Alaska to the warm islands of Hawaii. It has the Grand Canyon, the Mississippi River and Yellowstone, and about 342 million people live there.
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Watch
Country
Canada
Canada is the second-largest country in the world, stretching across the north of North America from the Atlantic to the Pacific and up into the Arctic. It has the Rocky Mountains, thousands of islands and about 42 million people, who speak English, French and many other languages.
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Watch
Country
New Zealand
New Zealand, also called Aotearoa, is an island country in the South Pacific. Its two main islands have snowy mountains, glaciers, volcanoes and deep fiords, and about 5.36 million people lived there in 2026.
Explore next
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Chinook salmon
The Chinook salmon, also called the king salmon, is the largest Pacific salmon. It hatches in a cold river, travels to the ocean to feed and grow for a few years, then swims back up its home river to lay eggs.
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Watch
3D
Animal
Sockeye salmon
The sockeye salmon is a Pacific salmon that usually grows up in a lake, spends a few years in the North Pacific Ocean, and then returns to the place it hatched to lay its eggs. On the way home it turns bright red with a green head.
-
Watch
Country
United States
The United States is a large country in North America made of 50 states, from icy Alaska to the warm islands of Hawaii. It has the Grand Canyon, the Mississippi River and Yellowstone, and about 342 million people live there.
-
Watch
Country
Canada
Canada is the second-largest country in the world, stretching across the north of North America from the Atlantic to the Pacific and up into the Arctic. It has the Rocky Mountains, thousands of islands and about 42 million people, who speak English, French and many other languages.
-
Watch
Country
New Zealand
New Zealand, also called Aotearoa, is an island country in the South Pacific. Its two main islands have snowy mountains, glaciers, volcanoes and deep fiords, and about 5.36 million people lived there in 2026.
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Alligator gar
The alligator gar is one of the largest freshwater fish in North America. It has a broad snout lined with teeth, armor-like scales, and a swim bladder that works like a lung, so it can gulp air in warm, still water. It lives in the big rivers, swamps and bayous of the southern United States, Mexico and Central America.
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Arapaima
The arapaima is one of the biggest freshwater fish in the world, longer than a grown-up is tall. It lives in the warm, slow rivers and flooded lakes of the Amazon, and it must swim up to the surface to gulp air every few minutes.
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Atlantic bluefin tuna
The Atlantic bluefin tuna is the largest of all tunas: big ones can be about 4 meters long. Its torpedo-shaped body is built for long journeys, and it can keep its body warmer than the water around it. Bluefin tuna were badly overfished, but with fishing limits set by countries working together, the numbers caught are now controlled.
For parents & teachers
What children will learn
- Describe how to recognize a rainbow trout (pink band, black spots, mouth ending behind the eye).
- Explain the difference between resident rainbow trout and steelhead.
- Describe the rainbow trout life cycle and compare it with salmon that die after spawning.
- Discuss why introducing a fish to new places can help anglers but harm native species.
Recommended ages: 3 to 17 · About 15 minutes
Talk about it
- Why might it help a species to have some fish that stay home and some that travel?
- What could go wrong when people release a fish into a river where it never lived before?
- How could a road culvert or a dam stop a trout from reaching its home stream?
Try at home or in class
- Lay a ruler or tape measure on the floor and mark 46 and 61 centimeters (18 and 24 inches): the usual length of a steelhead.
- Draw a trout and label the pink stripe, the black spots, the eye and the anal fin, then compare it with a salmon picture.
Key vocabulary: steelhead, redd, fry, hatchery, introduced, iteroparous
Where these facts come from
- The IUCN Red List of Threatened Species , International Union for Conservation of Nature (IUCN terms of use (no redistribution of Red List data or range maps))
- GBIF Backbone Taxonomy and GBIF Occurrence Search , Global Biodiversity Information Facility (CC0 1.0 (backbone); occurrence counts are facts derived from records under CC0, CC BY and CC BY-NC)
- Wikidata , Wikimedia Foundation (CC0 1.0)
- Oncorhynchus mykiss (Rainbow Trout), assessment 2024 , IUCN Red List of Threatened Species
- Rainbow Trout (Wildlife Notebook Series) , Alaska Department of Fish and Game
- Rainbow trout (Oncorhynchus mykiss) , US Fish and Wildlife Service
- Steelhead , NOAA Fisheries
- Rainbow trout (Oncorhynchus mykiss) fact sheet , US Geological Survey, Nonindigenous Aquatic Species
- Introductions of Oncorhynchus mykiss , FishBase
- Wikimedia Commons , Wikimedia Foundation (Per file: Public domain, CC0, CC BY or CC BY-SA only (credited on each page))
Checked, not yet human-reviewed. Last updated October 28, 2026. Spotted a mistake? Tell us.
Picture credits
- Photo: USFWS Mountain-Prairie, public domain, via Wikimedia Commons · source