Trout


  • Trout is the common name for a number of species of freshwater fish belonging to the genera Oncorhynchus, Salmo and Salvelinus, all of the subfamily Salmoninae
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  • 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 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.

    Description

    Resident freshwater rainbow trout adults average between 1 and 5 lb (0.5 and 2.3 kg) in riverine environments, while lake-dwelling and anadromous forms may reach 20 lb (9 kg). Coloration varies widely between regions and subspecies. Adult freshwater forms are generally blue-green or olive green with heavy black spotting over the length of the body. Adult fish have a broad reddish stripe along the lateral line, from gills to the tail, which is most pronounced in breeding males.[9] The caudal fin is squarish and only mildly forked. Lake-dwelling and anadromous forms are usually more silvery in color with the reddish stripe almost completely gone. Juvenile rainbow trout display parr marks (dark vertical bars) typical of most salmonid juveniles. In some redband and golden trout forms parr marks are typically retained into adulthood.[17] Some coastal rainbow trout (O. m. irideus) and Columbia River redband trout (O. m. gairdneri) populations and cutbow hybrids may also display reddish or pink throat markings similar to cutthroat trout.[18] In many regions, hatchery-bred trout can be distinguished from native trout via fin clips.[19] Fin clipping the adipose fin is a management tool used to identify hatchery-reared fish.[20]

    Life cycle

    Rainbow trout, including steelhead forms, generally spawn in early to late spring (January to June in the Northern Hemisphere and September to November in the Southern Hemisphere) when water temperatures reach at least 42 to 44 °F (6 to 7 °C).[21] The maximum recorded lifespan for a rainbow trout is 11 years.

    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 production of sufficient food sources. Lake populations generally require access to gravelly bottomed streams to be self-sustaining.[23]

    Spawning sites are usually a bed of fine gravel in a riffle above a pool. A female trout clears a redd in the gravel by turning on her side and beating her tail up and down. Female rainbow trout usually produce 2000 to 3000 4-to-5-millimetre (0.16 to 0.20 in) eggs per kilogram of weight.[24] During spawning, the eggs fall into spaces between the gravel, and immediately the female begins digging at the upstream edge of the nest, covering the eggs with the displaced gravel. As eggs are released by the female, a male moves alongside and deposits milt (sperm) over the eggs to fertilize them. The eggs usually hatch in about four to seven weeks although the time of hatching varies greatly with region and habitat. Newly hatched trout are called sac fry or alevin. In approximately two weeks, the yolk sac is completely consumed and fry commence feeding mainly on zooplankton. The growth rate of rainbow trout is variable with area, habitat, life history and quality and quantity of food.[25] As fry grow, they begin to develop “parr” marks or dark vertical bars on their sides. In this juvenile stage, immature trout are often called “parr” because of the marks. These small juvenile trout are sometimes called fingerlings because they are approximately the size of a human finger. In streams where rainbow trout are stocked for sport fishing but no natural reproduction occurs, some of the stocked trout may survive and grow or “carryover” for several seasons before they are caught or perish.[26]

    Steelhead life cycle

    The oceangoing (anadromous) form, including those returning for spawning, are known as steelhead in Canada and the U.S.[27] In Tasmania they are commercially propagated in sea cages and are known as ocean trout, although they are the same species.[28]

    Like salmon, steelhead return to their original hatching grounds to spawn. Similar to Atlantic salmon, but unlike their Pacific Oncorhynchus salmonid kin, steelhead are iteroparous (able to spawn several times, each time separated by months) and make several spawning trips between fresh and salt water, although fewer than 10 percent of native spawning adults survive from one spawning to another.[29] The survival rate for introduced populations in the Great Lakes is as high as 70 percent. 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 sea water.[30] There are genetic differences between freshwater and steelhead populations that may account for the smoltification in steelheads.[31]

    Juvenile steelhead may remain in the river for one to three years before smolting and migrating to sea. Individual steelhead populations leave the ocean and migrate into their freshwater spawning tributaries at different times of the year. Two general forms exist—”summer-run steelhead” and “winter-run steelhead”. Summer-run fish leave the ocean between May and October, before their reproductive organs are fully mature. They mature in fresh water while en route to spawning grounds where they spawn in the spring. Summer-run fish generally spawn in longer, more inland rivers such as the Columbia River. Winter-run fish are ready to spawn when they leave the ocean, typically between November and April, and spawn shortly after returning to fresh water. Winter-run fish generally spawn in shorter, coastal rivers typically found along the Olympic Peninsula and British Columbia coastline,[21] and summer-run fish are found in some shorter, coastal streams.[32] Once steelhead enter riverine systems and reach suitable spawning grounds, they spawn just like resident freshwater rainbow trout.

    Feeding

    Rainbow trout are predators with a varied diet and will eat nearly anything they can capture. They are not as piscivorous or aggressive as brown trout or chars. Rainbow trout, including juvenile steelhead in fresh water, routinely feed on larval, pupal and adult forms of aquatic insects (typically caddisflies, stoneflies, mayflies and aquatic diptera). They also eat fish eggs and adult forms of terrestrial insects (typically ants, beetles, grasshoppers and crickets) that fall into the water. Other prey include small fish up to one-third of their length, crayfish, shrimp, and other crustaceans. As rainbow trout grow, the proportion of fish consumed increases in most populations. Some lake-dwelling forms may become planktonic feeders. In rivers and streams populated with other salmonid species, rainbow trout eat varied fish eggs, including those of salmon, brown and cutthroat trout, mountain whitefish and the eggs of other rainbow trout. Rainbows also consume decomposing flesh from carcasses of other fish. Adult steelhead in the ocean feed primarily on other fish, squid and amphipods.[33]

    Range

    Native range of steelhead, the anadromous form of O. mykiss

    The native range of Oncorhynchus mykiss is in the coastal waters and tributary streams of the Pacific basin, from the Kamchatka Peninsula in Russia, east along the Aleutian Islands, throughout southwest Alaska, the Pacific coast of British Columbia and southeast Alaska, and south along the west coast of the U.S. to northern Mexico. It is claimed that the Mexican forms of Oncorhynchus mykiss represent the southernmost native range of any trout or salmon (Salmonidae),[34] though the Formosan landlocked salmon (O. masou formosanus) in Asia inhabits a similar latitude. The range of coastal rainbow trout (O. m. irideus) extends north from the Pacific basin into tributaries of the Bering Sea in northwest Alaska, while forms of the Columbia River redband trout (O. m. gairdneri) extend east into the upper Mackenzie River and Peace River watersheds in British Columbia and Alberta, Canada, which eventually drain into the Beaufort Sea, part of the Arctic Ocean.[35] Since 1875, the rainbow trout has been widely introduced into suitable lacustrine and riverine environments throughout the United States and around the world. Many of these introductions have established wild, self-sustaining populations.[36]

  • The cutthroat trout (Oncorhynchus clarkii) is a fish species of the family Salmonidae native to cold-water tributaries of the Pacific Ocean, Rocky Mountains
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  • and grey trout. In Lake Superior, it can also be variously known as siscowet, paperbelly and lean. The lake trout is prized both as a game fish and as a
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  • cutthroat trout and red-throated trout is a subspecies of the cutthroat trout (Oncorhynchus clarki) and is a freshwater fish in the salmon family (family
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  • The Apache trout, Oncorhynchus apache, is a species of freshwater fish in the salmon family (family Salmonidae) of order Salmoniformes. It is one of the
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  • The brook trout (Salvelinus fontinalis) is a species of freshwater fish in the salmon family Salmonidae. It is native to Eastern North America in the
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  • accounts in letters and diaries refer to them as “mountain trout” or “speckled trout.” The fish may have begun to disappear from the upper Muddy Creek in
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  • Trout tickling is the art of rubbing the underbelly of a trout with fingers. If done properly, the trout will go into a trance after a minute or so, and
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  • The brown trout (Salmo trutta) is a European species of salmonid fish that has been widely introduced into suitable environments globally. It includes
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  • fur to maintain its body heat. Tales of furry fish date to the 17th-century and later the “shaggy trout” of Iceland. The earliest known American publication
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  • impassible fish barriers, such as dams. Bull trout populations are also in danger from hybridization with non-native brook trout. They are a prized game fish in
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  • confused with cutthroat trout (Oncorynchus clarki). Redband trout are prized game fish. Throughout their distribution, the redband trout have been facing declines
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  • cutthroat trout (Oncorhynchus clarki utah) is a subspecies of cutthroat trout native to tributaries of the Great Salt Lake, U.S.A. Most of the fish‘s current
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  • Golden Trout Creek (tributary to the Kern River), Volcano Creek (tributary to Golden Trout Creek), and the South Fork Kern River. It is the state fish of
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  • Species Act. It was adopted as the state fish of Colorado on March 15, 1994 replacing the unofficial rainbow trout. The greenback cutthroat’s maximum size
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  • submarines of the United States Navy have been named USS Trout for the trout fish: USS Trout (SS-202), a Tambor-class submarine, was lost during World
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  • Locally, the fish is known as koran in Albanian and охридска пастрмка (ohridska pastrmka) in Macedonian. Ohrid trout is part of the brown trout complex,
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  • by the Game and Fish departments in New Mexico and Arizona, the US Forest Service and the US Fish and Wildlife Service, the Gila trout was down-listed
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  • The Biwa trout (Oncorhynchus rhodurus) is an anadromous salmonid fish of the genus Oncorhynchus, endemic to Lake Biwa in Shiga Prefecture, Japan, but also
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