Because of variations in their life history pattern and the habitat in which they spend the majority of their adult lives, rainbow trout (Salmo gairdneri) can be subdivided into three basic ecological forms: (1) anadromous steel head trout; (2) resident stream rainbow trout; and (3) lake or reservoir dwelling rainbow trout. It is important to recognize that there is a genetic or hereditary basis for each ecological form. For example, a "Lake or reservoir" rainbow may react very di fferent ly to envi ronmental stimuli associated with survival, feeding, and growth if it belongs to a population that has been evolving and adapting to the particular lake for hundreds or thousands of years, when compared to hatchery rainbow trout that have just been released in the lake.
Nonanadromous rainbow trout are native to the Pacific Coast drainages
inland as far,as the Rockies and from the Rio del Presidio River in Mexico to
the Kuskokwim River in Southwestern Alaska. They are also native to the Peace River drainage of British Columbia and the headwaters of the Athabaska River (of the McKenzie River basin) in Alberta. Their present range extends from the Arctic Circle to 550 S latitude.
They are perhaps the most widely introduced fish species; the only continent
lacking rainbow trout is Antarctica. Rainbow trout occur from 0 to 4,500 mabove sea level. Anadromous steel head trout are di stri buted along the Pacific coast from the Santa Ynez Mountains, California, to the Alaska Peninsula. Large rainbow trout on and north of the Alaska Peninsula appear to be nonanadromous.
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