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Fish Facts  »  Rainbow Trout


Physical description varies widely with sex, age, and habitat. In general, they are streamlined, with 8 to 12 spines in the anal fin and lack teeth at the base of the tongue (unlike their close relatives, Oncorhynchus clarkii). The undersides tend to be silvery with a pinkish red stripe along the upper-middle part of the body, though this stripe can vary from dark to light. Resident rainbows and spawning steelhead tend to be lighter with more pronounced pink stripes, while ocean-going steelhead are darker and silvery to blend into their ocean environment. Most have black spots above the lateral line, and resident rainbows tend to have more intense spotting, well below the lateral line. Juvenile fish have 8 to 13 parr marks on their sides and become silvery as they mature.


Freshwater, brackish, or marine waters of temperate zones. The anadromous form, called steelhead, spawn and complete their early development in freshwater mountain streams, then migrate to spend their adult life in the ocean. In freshwater, they prefer cool water but have been known to tolerate water temperatures up to 24°C (native climates have water temperatures around 12°C in the summer). Productive streams have a good mixture of riffles and pools and overhanging vegetation for shade. Most importantly, they require gravel beds to lay their eggs, and therefore, are sensitive to sedimentation and channel scouring. Juvenile trout prefer protective cover and low velocity water and have been known to be swept away and killed in water that is too fast. Since they are native to the western U.S., then tend to be found in coastal streams and rivers which naturally have reduced flow in summer months.


Rainbow trout are predators with a varied diet, and will eat nearly anything they can grab, in contrast to the legendary, selective image people often have of the fish's dietary habits. Rainbows are not quite as piscivorous or aggressive as the brown trout or lake trout (char). When young, insects make up a large portion of the diet, smaller fish (up to 1/3 of their length), along with crayfish and other crustaceans make up the remainder. As they grow, though, the proportion of fish increases in most all populations. Some lake dwelling lines may become planktonic feeders. While in flowing waters populated with salmon, trout will eat salmon eggs, salmon fry, and even salmon carcasses.


These fish are one of the most popular game fishes around the world, leading to nearly global introduction. They are introduced to stimulate local angling and associated recreational economies. However, where they are introduced, they can outcompete native trout species.


Rainbow trout are generally 20 to 30 in (51 to 76 cm) in length and on average weigh 8 lbs (3.6 kg)


Oncorhynchus mykiss are only native to the Pacific Coast of North America, extending from Alaska down to the border between California and Mexico. However, they have been introduced throughout the United States. and in every continent except for Antarctica for game fishing purposes. There are two forms: freshwater resident and anadromous. The resident form is commonly called rainbow trout while the anadromous form is called steelhead.


Wikipedia, University of Michigan Museum of Zoology Animal Diversity Web

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