Rainbow trout

Oncorhynchus mykiss

• Taxon: Freshwater fish
• Range: Native to the Western United States; introduced throughout North America
• Status: Not listed under the Endangered Species Act

Rainbow trout are coldwater fish that have long been associated with clear, healthy mountain streams and lakes in North America. Because of their ability to thrive in hatcheries, rainbow trout have been introduced into much of the United States and now inhabit many streams and lakes throughout the country. The popularity of rainbow trout among anglers has placed it among the top five sport fishes in North America, and it is considered by many to be the most important game fish west of the Rocky Mountains.

However, reduction of good quality trout habitat due to streambank and upland soil erosion, loss of riverside vegetation, water diversion, logging and mining activities, and pollution from municipal development and agriculture have significantly reduced the distribution and abundance of rainbow trout. In addition, construction of dams, road crossings, and other structures impede the ability of rainbow trout to migrate upstream and downstream, which is critical to successful completion of their life cycles. Consequently, nine different populations of steelhead (sea-run rainbow trout) have been added to the federal endangered species list.

Appearance

Rainbow trout are a North American game fish that get their name from the beautiful colors that shine on their skin. Coloration of the fish varies widely in relationship to sex, habitat, and maturity. Colors on the back of the fish can range from brown to olive to dark blue. Fish have a pinkish stripe/band running the length of their bodies, with a silvery underside that fades to pearl white. They have small black spots on their backs, fins, and tail. Average mature fish are around 16 inches long and weigh between 2 and 8 pounds. (The largest rainbow ever caught, however, was in Canada and weighed 48 pounds.)

Habitat

Rainbow trout can easily adapt to various aquatic habitats and environments. They prefer cool freshwater streams with gravel bottoms and natural cover, such as downed trees and boulders. These fish prefer water temperatures of 55 to 60 degrees Fahrenheit, but can tolerate temperatures that vary from 32 to 70 degrees Fahrenheit.

Diet

Rainbow trout are opportunistic feeders and will eat anything from aquatic and terrestrial insects, to fish eggs, to small minnows, to crustaceans and worms.

Historical range

The historical range of rainbow trout extends from Alaska to Mexico and includes British Columbia, Washington, Oregon, California, Idaho, and Nevada. Rainbow trout found primarily east of the Cascade Mountains in the U.S. and in the Upper Fraser River of British Columbia are often called redbands. Native rainbow trout are generally found in watersheds west of the Cascades.

Most rainbow trout found outside their historical range are “domesticated” steelhead.

Current range

Due to popularity as a game fish, they have been introduced into streams and lakes all over North America.

Conservation challenges

Whirling disease has developed in the last several decades and is a threat to trout fisheries across the United States. Primarily affecting hatchery-raised rainbow trout and other salmonids, whirling disease is caused by a microscopic parasite that causes fingerling trout to grow with badly curved spines and other skeletal deformities that can result in high fingerling mortality. Found in 22 states to date, whirling disease made its most significant appearance in wild waters in 1994 in Colorado (upper Colorado River) and Montana (Madison River). Significant efforts are being made to understand whirling disease through research and management of hatchery-raised rainbow trout and wild trout populations with the goal of protecting rainbow trout and other native trout fisheries nationwide.

Federal Register notices

The following Federal Register documents were automatically gathered by searching the Federal Register Official API with this species’ scientific name ordered by relevance. You can conduct your own search on the Federal Register website.

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