Rainbow Trout

Rainbow Trout
Rainbow Trout



The Rainbow Trout (Oncorhynchus mykiss) is one of the best known and widespread fish species in the world. They are torpedo-shaped and usually blue-green to yellow-green with a prominent pink streak along most of each side. Their underbelly is white and there are small black spots starting from just under the pink streak up and over the rest of the body as well as over the head, dorsal fin and tail.

A length of 20 to 30 inches is typical and a weight of about eight pounds is common. As they grow they get heavier faster than they get longer. They have reached over four feet and a record weight of 57 pounds. Normal life span is four to six years, but that record fish was estimated to be eleven years old.

A Type of Salmon
Rainbow trout can live in a wide range of habitats from rivers and streams to ponds, lakes and reservoirs. They feed on aquatic and terrestrial insects, fish eggs, fish fry and smaller fish (up to a third their own length), freshwater shrimp (scuds) as well as crayfish and other crustaceans and even plankton. They spawn in the spring, usually April or May, in running water. This all applies to Bighorn Canyon and this region of the country, but it is really more complicated than this.

Rainbow Trout are considered native to the tributaries of the Pacific Ocean in Asia and North America. A range map would be able to use the Continental Divide as the eastern boundary for the range of native Rainbow Trout in North America. In fact they are a type of salmon and many of them are anadromus. That means they swim out to sea and live there several years until they return up to the stream of their birth in order to spawn. The anadromus individuals lose the distinctive pink streak and have a silverfish appearance and are known as Steelhead, but they are the same species of Rainbow Trout. Steelheads can rejuvenate after spawning so they may return to the ocean and repeat the anadromus cycle.

Food and Sport
They have been introduced for both food and sport into over 45 countries and every continent except Antarctica. They are fish farmed and also raised in ocean cages. Often able to out-compete native species in areas where they have been introduced or feeding directly on those species, they can be considered an exotic species, but they remain a very popular species for both food and sport.

Trout populations can be adversely affected by habitat loss due to dams, water being pumped from drainages for various uses, water pollution, and even confinement in concrete channels where water is pumped long distances for human use.

The Effects of Drought
The recent drought in our region left many spawning gravel beds high and dry. The most critical times for the Rainbow Trout are during spawning in April and May, but these are often the same times most affected by the amount and timing of the runoff of the winter snow pack and the spring rains when we get a significant portion of the year’s precipitation.

Managing to meet the multiple uses of power generation, irrigation, flood control, recreational boating levels and prime fish habitat on one of the best trout streams in the country requires knowing how much water is in the system now, how much there will be at various times in the future and how warm it is going to be and when during the runoff.

But when there is not much water to manage, such as from 2000 to 2005, the trout populations are sure to suffer. With more water, hopefully the upward trends in trout populations will continue.

Last updated: February 24, 2015

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Bighorn Canyon National Recreation Area South District Visitor Center
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