Rainbow trout

Rainbow trout
Photo of hand holding adult female rainbow trout
Adult female rainbow trout
Scientific classification e
Kingdom:Animalia
Phylum:Chordata
Class:Actinopterygii
Order:Salmoniformes
Family:Salmonidae
Genus:Oncorhynchus
Species:O. mykiss
Binomial name
Oncorhynchus mykiss
(Walbaum, 1792)
Synonyms[1]

The rainbow trout (Oncorhynchus mykiss) is a trout and species of salmonid native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coastal rainbow trout (O. m. irideus) or Columbia River redband trout (O. m. gairdneri) that usually returns to fresh water to spawn after living two to three years in the ocean. Freshwater forms that have been introduced into the Great Lakes and migrate into tributaries to spawn are also called steelhead.

Adult freshwater stream rainbow trout average between 1 and 5 lb (0.5 and 2.3 kg), while lake-dwelling and anadromous forms may reach 20 lb (9 kg). Coloration varies widely based on subspecies, forms and habitat. Adult fish are distinguished by a broad reddish stripe along the lateral line, from gills to the tail, which is most vivid in breeding males.

Wild-caught and hatchery-reared forms of this species have been transplanted and introduced for food or sport in at least 45 countries and every continent except Antarctica. Introductions to locations outside their native range in the United States (U.S.), Southern Europe, Australia, New Zealand and South America have damaged native fish species. Introduced populations may affect native species by preying on them, out-competing them, transmitting contagious diseases (such as whirling disease), or hybridizing with closely related species and subspecies, thus reducing genetic purity. The rainbow trout is included in the list of the top 100 globally invasive species. Nonetheless, other introductions into waters previously devoid of any fish species or with severely depleted stocks of native fish have created sport fisheries such as the Great Lakes and Wyoming's Firehole River.

Some local populations of specific subspecies, or in the case of steelhead, distinct population segments, are listed as either threatened or endangered under the Endangered Species Act. The steelhead is the official state fish of Washington.[2]

Taxonomy

The scientific name of the rainbow trout is Oncorhynchus mykiss.[3] 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. Walbaum's original species name, mykiss, was derived from the local Kamchatkan name used for the fish, mykizha. The name of the genus is from the Greek onkos ("hook") and rynchos ("nose"), in reference to the hooked jaws of males in the mating season (the "kype").[4]

Sir John Richardson, a Scottish naturalist, named a specimen of this species Salmo gairdneri in 1836 to honor Meredith Gairdner, a Hudson's Bay Company surgeon at Fort Vancouver on the Columbia River who provided Richardson with specimens.[5] In 1855, William P. Gibbons, the curator of Geology and Mineralogy[6] at the California Academy of Sciences, found a population and named it Salmo iridia (Latin: rainbow), later corrected to Salmo irideus. These names faded once it was determined that Walbaum's description of type specimens was conspecific and therefore had precedence.[7] In 1989, morphological and genetic studies indicated that trout of the Pacific basin were genetically closer to Pacific salmon (Oncorhynchus species) than to the Salmosbrown trout (Salmo trutta) or Atlantic salmon (Salmo salar) of the Atlantic basin.[8] Thus, in 1989, taxonomic authorities moved the rainbow, cutthroat and other Pacific basin trout into the genus Oncorhynchus.[4] Walbaum's name had precedence, so the species name Oncorhynchus mykiss became the scientific name of the rainbow trout. The previous species names irideus and gairdneri were adopted as subspecies names for the coastal rainbow and Columbia River redband trout, respectively.[4] Anadromous forms of the coastal rainbow trout (O. m. irideus) or redband trout (O. m. gairdneri) are commonly known as steelhead.[3]

Subspecies

Subspecies of Oncorhynchus mykiss are listed below as described by fisheries biologist Robert J. Behnke (2002).[9]

Geographical group Common name Scientific name Range Image
Type subspecies Kamchatkan rainbow trout O. m. mykiss (Walbaum, 1792) Western Pacific: Kamchatka Peninsula, and has been recorded from the Commander Islands east of Kamchatka, and sporadically in the Sea of Okhotsk, as far south as the mouth of the Amur River
Coastal forms Coastal rainbow trout O. m. irideus (Gibbons, 1855) Pacific Ocean tributaries from Aleutian Islands in Alaska south to Southern California. Anadromous forms are known as steelhead, freshwater forms as rainbow trout. Lake Washington Ship Canal Fish Ladder pamphlet - ocean phase Steelhead.jpg
Lake Washington Ship Canal Fish Ladder pamphlet - male freshwater phase Steelhead.jpg
Ocean and fresh water forms of coastal rainbow trout; a.k.a. "steelhead"
O. m. irideus
Beardslee trout O. m. irideus var. beardsleei (not a true subspecies, but a genetically unique lake-dwelling variety of coastal rainbow trout) (Jordan, 1896)[10] Isolated in Lake Crescent, Washington
Redband forms Columbia River redband trout O. m. gairdneri (Richardson, 1836) Found in the Columbia River and its tributaries in Montana, Washington and Idaho. Anadromous forms are known as redband steelhead.
Columbia River redband trout
O. m. gairdneri
Athabasca rainbow trout O. m. spp., considered by Behnke as a form of O. m. gairdneri, but considered a separate subspecies by biologist L. M. Carl of the Ontario Ministry of Resources, Aquatic Ecosystems Research Section and associates from work published in 1994.[11] Distributed throughout the headwaters of the Athabasca River system in Alberta
McCloud River redband trout O. m. stonei (Jordan, 1894) Native to the McCloud River, upstream of Middle Falls, and its tributaries in Northern California, south of Mount Shasta.
Sheepheaven Creek redband trout O. m. spp. Native to Sheepheaven Creek, Siskiyou County, California. Sheepheaven Creek redband were transplanted into Swamp Creek in 1972 and 1974 and into Trout Creek in 1977.
Great Basin redband trout O. m. newberrii (Girard, 1859) Native in southeastern Oregon and parts of California and Nevada on the periphery of the Great Basin.
Eagle Lake trout O. m. aquilarum (Snyder, 1917) Endemic to Eagle Lake in Lassen County, California.
Kamloops rainbow trout O. m. kamloops strain (Jordan, 1892) Native to several large British Columbia lakes, particularly Kamloops Lake and Kootenay Lake. Known for its very large size.
Kern River golden trout Golden trout O. m. aguabonita (Jordan, 1892) Native to Golden Trout Creek (tributary to the Kern River), Volcano Creek (tributary to Golden Trout Creek), and the South Fork Kern River. Goldentroutwiki.jpg
Kern River golden trout
O. m. aguabonita
Kern River rainbow trout O. m. gilberti (Jordan, 1894) Endemic to the Kern River and tributaries in Tulare County, California. Its current range is drastically reduced from its historic range. Remnant populations live in the Kern River above Durrwood Creek, in upper Ninemile, Rattlesnake and Osa creeks, and possibly in upper Peppermint Creek.
Little Kern golden trout O. m. whitei (Evermann, 1906) Endemic to about 100 miles (160 km) of the Little Kern River and tributaries. Their current range is restricted to five headwater streams in the Kern River basin (Wet Meadows, Deadman, Soda Spring, Willow, Sheep and Fish creeks) plus an introduced population in Coyote Creek, a tributary of the Kern River.[12]
Mexico forms Mexican rainbow trout
Rio Yaqui, Rio Mayo and Guzman trout
Rio San Lorenzo and Arroyo la Sidra trout
Rio del Presidio trout
O. m. nelsoni (Evermann, 1908) Sometimes referred to as Nelson's trout, occurs in three distinct geographic groups. The taxonomy of these trout is subject to ongoing research and there may be significant diversity of forms in this group.[13]
Mutated forms Golden rainbow trout
Palomino trout
So-called golden rainbow trout or palomino trout are bred from a single mutated color variant of O. mykiss that originated in a West Virginia fish hatchery in 1955.[14][15] Golden rainbow trout are predominantly yellowish, lacking the typical green field and black spots but retaining the diffuse red stripe.[15] The palomino trout is a mix of golden and common rainbow trout, resulting in an intermediate color. The golden rainbow trout is not the same subspecies as the naturally occurring O. m. aguabonita, the Kern River golden trout of California.[15] Golden Rainbow Trout Cropped.jpg
Golden rainbow trout[16]
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