Rainbow trout
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? Oncorhynchus
mykiss |
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 Rainbow
Trout
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| Oncorhynchus
mykiss Walbaum, 1792 |
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The rainbow trout (Oncorhynchus mykiss, a.k.a. Salmo iridia), also called steelhead trout, is a single species of trout native to the Pacific Ocean and in North American rivers and lakes west of the Rocky Mountains. Rainbow trout are now worldwide in distribution and are a highly prized game fish. Rainbow trout have been introduced to at least 45 countries, and every continent except Antarctica. However, in some of these locations, such as Australia, rainbow trout have had very serious negative impacts on native fish species.
The naming of the rainbow trout species was based on fish taken from the San Leandro Creek drainage in Oakland, California. In 1855, Dr. W.P. Gibbons, founder of the California Academy of Sciences, was given three specimens obtained from the creek. He described and assigned them the scientific name Salmo iridia. It was later determined that Gibbons and Walbaum were referring to the same species, and the original binomial name is now used to refer to the species.
Physical characteristics
Rainbow trout are the smaller variety, found only in fresh water. Steelhead spend their adult lives in the ocean, but return to spawn in the streams in which they were hatched. They occur in cool streams up to 4500 m in elevation.
Rainbows and steelhead have small black spots along their back, dorsal fin and caudal fin. Rainbows have a pink streak that runs from the gill cover to the caudal fin. The colour of a rainbow's back varies from blue or green to a yellow-green or brown. Steelhead usually lack the pink stripe, except when young or spawning, and have chrome-colored sides. Rainbows are distinguished from their cousins, the cutthroat trout, by their short maxilla, which reaches to, but not past the rear margin of the eye. Rainbow trout also lack hyoid teeth, a feature present in cutthroat trout.
Rainbows range from 30 to 45 cm (12 to 18 inches) in length. Steelheads grow longer, ranging from 50 to 100 cm (20 to 40 inches) in length. Steelhead range in weight from 2.5 kg to 10 kg.
Lifecycle
Like salmon, steelhead are anadromous: they return to their original hatching ground to spawn. 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. Unlike salmon, steelhead are iteroparous and may make several spawning trips between fresh and salt water.
Redband trout, sometimes called "Redsides," are another subspecies of rainbow trout and are typically found further inland than regular rainbow trout.
Rainbow trout as food
Rainbow trout is popular in Western cuisine and is often farmed for food. It has tender flesh and a mild, somewhat nutty flavour. However, farmed trout and those taken from certain lakes have a pronounced muddy flavour which many people find unappealing; many shoppers therefore make it a point to ascertain the source of the fish before buying.
Clear Springs Foods, located near Buhl, Idaho, processes over 20 million pounds (9000 t) of Rainbow Trout each year, making it the world's largest producer.