[4] The species was originally named by German naturalist and taxonomist Johann Julius Walbaum in 1792 based on type specimens from the Kamchatka Peninsula in Siberia.

[24] Freshwater resident rainbow trout usually inhabit and spawn in small to moderately large, well-oxygenated, shallow rivers with gravel bottoms.

They are native to the alluvial or freestone streams that are typical tributaries of the Pacific basin but introduced rainbow trout have established wild, self-sustaining populations in other river types such as bedrock and spring creeks.

Lake-resident rainbow trout are usually found in moderately deep, cool lakes with adequate shallows and vegetation to support the production of sufficient food sources.

[28] The oceangoing (anadromous) form, including those returning for spawning, are known as steelhead in Canada and the U.S.[29] In Tasmania they are commercially propagated in sea cages and are known as ocean trout, although they are the same species.

As young steelhead transition from freshwater to saltwater, a process called "smoltification" occurs where the trout undergoes physiological changes to allow it to survive in seawater.

High metabolic activity has been correlated with increased levels of oxidative stress [35][36] and decreased machinery repair [37] in rainbow trout.

During high oxidative stress, the mitochondria are the most important organelle contributing to tissue damage because of their role in metabolism and production of reactive oxygen species.

In a study done by Almaida-Pagàn et al.,[38] researchers identified changes to the heart and brain mitochondrial membrane phospholipid composition in rainbow trout due to the differing levels of oxidative stress each organ faced during a high-stress time such as rapid growth and development.

During the trout's development into an adult, a time of intense growth, the mitochondrial membrane composition and fluidity changes, which can cause defects in the electron transport chain.

These defects combined with altered machinery repair and reactive oxygen species may cause more detrimental effects on the mitochondria in the fish as it matures.

They also eat fish eggs and adult forms of terrestrial insects (typically ants, beetles, grasshoppers, and crickets) that fall into the water, as well as algae.

Inland production of rainbow trout to supply domestic markets has increased in countries such as Italy, France, Germany, Denmark, and Spain.

[53][59] Rainbow trout farming is one of the largest finfish aquaculture industries in the U.S.[53] They are raised inland in facilities where raceways or ponds have continuously flowing water with little pollution and a low risk of escape.

[60] There have been recent interest and efforts in introducing a rainbow trout species that can be completely fed on a vegan diet through genetic selection.

As a consequence, some rainbow populations, particularly anadromous forms within their native range, have been classified as endangered, threatened or species of special concern by federal or state agencies.

beardsleei), a genetically unique lake-dwelling variety of the coastal rainbow trout that is isolated in Lake Crescent (Washington), is threatened by the loss of its only spawning grounds in the Lyre River to siltation and other types of habitat degradation.

[77] It was first described in rainbow trout introduced to Germany a century ago, but its range has spread and it has appeared in most of Europe, northern Asia, the U.S., South Africa[78] and other countries.

Having no innate immunity to M. cerebralis, rainbow trout are particularly susceptible, and can release so many spores that even more resistant species in the same area, such as Salmo trutta, can become overloaded with parasites and incur mortalities of 80 to 90 percent.

[81][82] The parasite M. cerebralis was first recorded in North America in 1956 in Pennsylvania,[80] but until the 1990s, whirling disease was considered a manageable problem affecting only rainbow trout in hatcheries.

It eventually became established in the natural waters of the Rocky Mountain states (Colorado, Wyoming, Utah, Montana, Idaho, New Mexico), where it is damaging several sport fishing rivers.

[85] The New Zealand mud snail (Potamopyrgus antipodarum), once endemic to New Zealand, has spread widely and has become naturalised and an invasive species in many areas including Australia,[86] Asia (Japan,[87] in the Garmat Ali River in Iraq since 2008[88]), Europe (since 1859 in England), and North America (U.S. and Canada: Thunder Bay in Ontario since 2001, British Columbia since July 2007[87]), most likely inadvertently during human activity.

[90] There is evidence North American fishes are unable to digest the tiny but hard shells of the mud snail, and that their presence may result in poor growth outcomes for rainbow trout.

[92] Didymosphenia geminata, commonly known as didymo or rock snot, is a species of diatom that produces nuisance growths in freshwater rivers and streams with consistently cold water temperatures.

It is not considered a significant human health risk, but it can affect stream habitats and sources of food for fish, including rainbow trout, and make recreational activities unpleasant.

[100] Steelhead in the Kamchatka Peninsula are threatened by over-harvest, particularly from poaching and potential development, and are listed in the Red Data Book of Russia that documents rare and endangered species.

[27] There are tribal commercial fisheries for steelhead in Puget Sound, the Washington coast, and in the Columbia River, but there has been controversy regarding overharvesting of native stocks.

Many of these introductions have resulted in environmental and ecological problems, as the introduced rainbow trout disrupt local ecosystems and outcompete or prey upon indigenous fishes.

[108] Other introductions to support sport angling in waters either devoid of fish or with seriously depleted native stocks have created world-class fisheries such as in the Firehole River in Yellowstone National Park[109][110][111] and in the Great Lakes.

[115] Farmed rainbow trout are considered one of the safest fish to eat and are noted for high levels of vitamin B and a generally appealing flavor.