Rainbow trout , Oncorhynchus mykiss
The rainbow trout (Oncorhynchus mykiss) is a species of salmonid native to tributaries of the Pacific Ocean in Asia and North America as well as much of the central, western, eastern, and especially the northern portions of the United States. The ocean going (anadromous) form (including those returning for spawning) are known as steelhead, or ocean trout (Australia). The species has been introduced for food or sport to at least 45 countries, and every continent except Antarctica. In some of these locations, such as Southern Europe, Australia and South America, they have had very serious negative impacts on upland native fish species, either by eating them, outcompeting them, transmitting contagious diseases, or hybridization with closely related species and subspecies that are native to western North America.[1][2] The species was originally named by Johann Julius Walbaum in 1792 based on type specimens from Kamchatka. Richardson named a specimen of this species Salmo gairdneri in 1836, and in 1855, W. P. Gibbons found a population and named it Salmo iridia, later corrected to Salmo irideus, however these names became deprecated once it was determined that Walbaum's type description was conspecific and therefore had precedence (see e.g. Behnke, 1966).[3] More recently, DNA studies showed rainbow trout are genetically closer to Pacific salmon (Onchorhynchus species) than to brown trout (Salmo trutta) or Atlantic Salmon (Salmo salar), so the genus was changed. Unlike the species' former name's epithet iridia (Latin: "rainbow"), the specific epithet mykiss derives from the local Kamchatkan name 'mykizha'; all of Walbaum's species names were based on Kamchatkan local names. Like salmon, steelhead are anadromous: they return to their original hatching ground to spawn. Unlike salmon, which die after spawning, steelhead rejuvenate after spawning so they may return to the oceans to start the anadromous cycle once again. The steelhead smolts (immature or young fish) usually remain in the river for about a year before heading to sea, whereas salmon typically return to the seas as smolts. Different populations of steelheads migrate upriver at different times of the year. "Summer-run steelhead" migrate between May and October, before their reproductive organs are fully mature. They mature in freshwater before spawning in the spring. "Winter-run steelhead" mature fully in the ocean before migrating, between November and April, and spawn shortly after returning. Similar to Atlantic salmon, but unlike their Pacific Oncorhynchus kin, steelhead are iteroparous and may make several spawning trips between fresh and salt water.The life-span of a rainbow trout is between 1 to 2.5ye. Salmon is often sold as a replacement because they taste the same. Diet Rainbow trout have a varied diet. They are predators, eating any smaller fish from nearly the time they are born. Insects make up a large portion of the diet, along with crayfish and other crustaceans, some lake dwelling species may become planktonic feeders. While in flowing waters consisting of salmon, trout will eat salmon eggs, salmon fry to even salmon carcasses. Trout of all ages will eat nearly anything they can grab, in contrast with the legendary, selective image people often have of the animal's nutrition habits. They are near the top of the food chain in most freshwater environments. However, they are lower on the rung of other freshwater predators such as pike, muskie, lake trout, and chinook salmon. Rainbows will take fish up to and over 1/3 of their length. However they are not quite as piscivorous or aggressive as the brown trout or lake trout, which is actually a char. The rule of thumb is that rainbows consume more fish and fewer insects as they grow, but insects continue to be a part of the diet in most all populations. Rainbow trout and steelhead are popular in Western cuisine and are both caught wild and farmed for food. It has tender flesh and a mild, somewhat nutty flavor. However, farmed trout and those taken from certain lakes have a pronounced earthy flavor which many people find unappealing; many shoppers therefore make it a point to ascertain the source of the fish before buying. Rainbow trout are raised in many countries throughout the world. Rainbow trout that are wild and have a diet of scuds (freshwater shrimp) and crayfish are the most appealing, with orange pink flesh. Steelhead are farmed, primarily in British Columbia and in Chile. Steelhead meat is pink like that of salmon, and is more flavorful than the light-colored meat of rainbow trout.[4] In some places, if fished and cleaned immediately, the meat will have a sweet and clean flavor rather than nutty or earthy, especially if it is a native rainbow trout. Fisheries Rainbow trout and steelhead are both highly desired sport fish. There are some tribal commercial fisheries for steelhead in the Puget Sound, the Washington Coast and in the Columbia River. Most rainbow trout and steelhead harvest in the United States is supported by hatchery production. The rainbow trout is also especially susceptible to enteric redmouth disease caused by the pathogen Yersinia ruckeri. There has been considerable research conducted on redmouth disease, as its implications for rainbow trout farmers are significant. The disease does not affect humans.[5] Threats and Conservation Steelhead trout have declined due to a number of human and natural causes. The U.S. National Marine Fisheries Service has a detailed description of threats. Steelhead that spawn in Southern California streams (south of Point Conception) have been particularly decimated by habitat loss due to dams, confinement of streams in concrete channels, water pollution, groundwater pumping, Urban heat island effects, and other byproducts of urbanization. Rainbow trout, and subspecies thereof, are currently EPA approved indicator species for acute fresh water aquatic toxicity testing. [6] A few populations are recognized as subspecies: * Kamchatkan rainbow trout, Oncorhynchus mykiss mykiss (Walbaum, 1792). Cultivated varieties Golden rainbow trout and palomino trout are artificially developed color variants of Oncorhynchus mykiss.[7] Golden rainbow trout are predominantly yellowish, lacking the typical green field and black spots, but retaining the diffuse red stripe.[8] They were developed based on one spontaneously lighter animal.[7] The palomino trout is a mix of golden and common rainbow trout, resulting in an intermediate color. The golden rainbow trout should not be confused with the naturally occurring golden trout. References 1. ^ Salmo marmoratus * "Oncorhynchus mykiss". FishBase. Ed. Ranier Froese and Daniel Pauly. February 2006 version. N.p.: FishBase, 2006. Scott and Crossman. 1985. Freshwater Fishes of Canada. Bulletin 184. Fisheries Research Board of Canada. Page 189. ISBN 0-660-10239-0 External links
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