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Montana Field Guide

Montana Field Guides

Rainbow Trout - Oncorhynchus mykiss

Native Species

Global Rank: G5
State Rank: S5

Agency Status


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General Description
The rainbow trout is Montana's number one game fish. Rainbow trout were introduced from numerous hatchery stocks into virtually every suitable habitat in the state, beginning in 1889. Scientists believe that only the rainbow trout of the upper Kootenai River drainage are native to this state. This small group of natives are a Fish of Special Concern. Rainbow trout introductions have caused a severe reduction in the range of the native cutthroat trout through hybridization and competition. Rainbow trout fare well under a wide range of habitat conditions from ponds to reservoirs, lakes, and streams. Various strains of rainbow trout, like breeds of cattle, are used for different purposes. The state has stocked hundreds of millions of rainbow in state waters in the last 100 years. However, today the policies have evolved and rainbow trout are stocked primarily in lakes and reservoirs but no longer in streams. The state record for rainbow trout is over 33 pounds, and fish of up to 10 pounds are common in some of our most productive waters. Rainbow are efficient at feeding on plankton, aquatic and terrestrial insects, and occasionally some smaller fishes. They spawn in early spring in running water, usually April or May, and maintain themselves quite nicely if the habitat is not degraded.

Diagnostic Characteristics
Montana: both pure and moderately hybridized populations of westslope cutthroat trout have a high incidence of basibranchial teeth, whereas pure rainbow trout lack these teeth; presence of basibranchial teeth in some individuals of a rainbow trout population indicates hybridization with westslope cutthroat trout (Leary et al. 1996). Individuals living in large or turbid lakes or under ice tend to be iridescent silver.

Species Range
Montana Range

All Ranges
(Click legend blocks to view individual ranges)

Observations in Montana Natural Heritage Program Database
Number of Observations: 14989

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Migrates into tributary streams from lakes to spawn and river populations may also move upstream and/or into tributary streams.

Cool clean streams, lakes, res., farm ponds. Able to withstand wider range of temperatures than most trout. Spawns in streams over gravel beds (Brown 1971, Holton 1981).

Food Habits
Feed mainly on aquatic insects but eat what is available to them. Large adults also eat fish (Brown 1971). River populations mostly insect eaters while zooplankton and forage fish are important in Lake Koocanusa (Huston et al. 1984).

Populations of native and introduced rainbow trout as well as their hybrids coexist in Kootenai River drainage.

Reproductive Characteristics
Sexually mature 2-3 years but sometimes 1 year. Spawns April-July depending on water temperatures. Eggs hatch in 50 days at 50 degrees F. (Brown 1971). Young smolt at 0-2 years in tributaries and lake Koocanusa (Huston et al. 1984, May and Huston 1979).

  • Literature Cited AboveLegend:   View Online Publication
    • Brown, C.J.D. 1971. Fishes of Montana. Montana State University, Bozeman, MT. 207 pp.
    • Holton, G.D. 1981. Identification of Montana's most common game and sport fishes. Montana Outdoors reprint.
    • Huston J.E., P. Hamlin; B. May 1937-; Montana. Dept. of Fish, Wildlife, and Parks.; United States. Army. Corps of Engineers. Seattle District. 1984
    • Leary, R.F., W.R. Gould, and G.K. Sage. 1996. Success of basibranchial teeth in indicating pure populations of rainbow trout and failure to indicate pure populations of westslope cutthroat trout. North American Journal of Fisheries Management 16:210-213.
    • May, B.E. and J.E. Huston. 1979. Status of fish populations in the Kootenai River below Libby dam. Montana Department of Fish, Wildlife, and Parks. 57 pp.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Johnson, J. H. 1985. Comparative diets of Paiute sculpin, speckled dace, and subyearling steelhead trout in tributaries of the Clearwater River, Idaho. Northwest Sci. 59:1-9.
    • Land & Water Consulting, Inc., Missoula, MT., 2002, Montana Dept. of Transportation Wetland Mitigation Monitoring Report, Year 2001: Big Spring Creek, Lewistown, Montana. Proj. No. 130091.029. July 2002. In 2001 Wetland Mitigation Monitoring Reports, Vol. I.
    • Land & Water Consulting, Inc., Missoula, MT., 2002, Montana Dept. of Transportation Wetland Mitigation Monitoring Report, Year 2002: Big Spring Creek, Lewistown, Montana. Proj. No. 130091.029. February 2003. In 2002 Wetland Mitigation Monitoring Reports, Vol. I.
    • Olenick, R.J., J.H. Gee. 1981. Tiger Salamanders (Ambystoma tigrinum) and stocked rainbow trout (Salmo gairdneri): potential competitors for food in Manitoba prairie pothole lakes. Canadian Field Naturalist 95(2): 129-132.
    • Zackheim, K. 1973. Exhibit H: Wildlife Study. In Ash Grove Cement Co. files.
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Rainbow Trout — Oncorhynchus mykiss.  Montana Field Guide.  .  Retrieved on , from