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Montana Field Guide

Montana Field Guides

Brown Trout - Salmo trutta

Non-native Species

Global Rank: G5
State Rank: SNA

Agency Status


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General Description
The brown trout belongs to a different genus than our native trout species. They evolved in Europe and western Asia and were introduced to North America in 1883 and to Montana in 1889 in the Madison River. Today brown trout are found throughout most of Montana except the northwest and parts of the east. Generally, they prefer lower gradient, larger streams than cutthroat and rainbow, and they also do well in many reservoirs. Brown trout were widely stocked in the first half of this century, but today most come from natural reproduction. Brown trout are great competitors and generally are more tolerant of dewatering and other environmental disturbances than our other trout species. The state record is 29 pounds, and large fish are not at all uncommon, although 12-20 inches is the usual size range of adults. Brown trout spawn in gravel redds like our native trout but their spawning season is in the fall. This gives them a distinct advantage in some habitats since their spawning and incubation period lies outside the irrigation season. Brown trout are more predaceous than rainbow or cutthroat. Large fish often feed at night on other fish as well as crayfish and other invertebrates.

Diagnostic Characteristics
May lack red and orange spots. Black spots may be irregularly shaped or round. Spots with halos on gill covers are a clue that trout is a brown trout.

Species Range
Montana Range


Observations in Montana Natural Heritage Program Database
Number of Observations: 11796

(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)

May move upstream some distance or into tributary to spawn.

Valley portions of larger rivers where gradients are low and summer temperatures range from 60-70 degrees F. Also reservoirs and lakes at similar elevation with suitable spawning trib. (Brown 1971, Holton 1981).

Food Habits
Feeds largely on underwater aquatic insects. Also uses many other small organisms available and large individuals eat many small fish (Brown 1971).

Habitat requirements similar to brook trout, but brown trout can remain active and thriving at slightly higher temperatures (Scott and Crossman 1973).

Reproductive Characteristics
Sexually mature usually 3 years but sometimes 2,4, and 5 years. Spawns Oct.-Dec. Eggs laid in redd and hatch the following Spring. Febr.-April under natural conditions. Hatch in about 50 days at 50 degrees F. (Brown 1971).

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Citation for data on this website:
Brown Trout — Salmo trutta.  Montana Field Guide.  .  Retrieved on , from