Fish Description

Oncorhynchus spp.
Cutthroat-Rainbow Hybrid Trout, Cutbow

Family: Trout and Salmon (Salmonidae)

Order: Salmon/Trout/Pike (Salmoniformes)

General Description: Rainbow-cutthroat have silver to gold coloration on the flanks, green coloration on the back, and various patterns of dark spots on the tail, along the back, and sometimes on the head. Hybrid trout can look like rainbow trout, a cutthroat trout, or like an intermediate of the two. Hybrid fish with one parent from each species often have an obvious mixture of features from each species, such as a bright throat slash (cutthroat), a red stripe along the flanks (rainbow trout), and many spots on the head (rainbow trout).

Abundance: patchy

Origin: native

Size:
  • Average: 10in
  • Largest: 36in

Distribution: Rainbow-cutthroat hybrids occur anywhere rainbow trout have been stocked in or have invaded native cutthroat trout habitats. In Montana, rainbow-cutthroat hybrids occur in the native habitats of both westslope and yellowstone cutthroat trouts. Trout are typically found in clear and cool lakes, streams, and rivers.

Habitat: Rainbow-cutthroat hybrids are commonly found in streams, rivers, and lakes throughout western Montana. They are typically found in waters that are cold to cool and clear. Hybrid trout are most successful in streams with a variety of habitat components including pools, runs, riffles, undercut banks, and large woody debris.

Life History: Both rainbow trout and cutthroat trout are spring spawners. Since they are very similar fishes and eggs are fertilized externally, hybridization is possible where the two species overlap. Both species can reach sexual maturity as 2 year-olds. Both species also have several life history strategies. Some rainbow and cutthroat trout, called residents, will spend their entire lives in a small spawining tributary to larger river systems. Other trout will migrate to larger rivers to grow large and return to the stream where they were born (or a nearby stream) for spawning. In a third life-history strategy, trout will migrate to lakes in order to grow large before spawning.

Similar: Westslope cutthroat trout (Oncorhynchus clarki lewisi) have spots that are concentrated towards the tail and tend to occur above the lateral line. Westslope cutthroat trout also have red throat slashes. Juveniles of rainbow trout and westslope cutthroat trout are difficult to distinguish. Hybrids between rainbow trout and westslope cutthroat trout are common and genetic analysis is required for positive identification because hybrids can look like westslope cutthroat trout, rainbow trout, or a mixture of the two.

Did You Know: In most of Montana, rainbow-cutthroat trout hybrids are the result of non-native rainbow trout breeding with native cutthroat trout. Rainbow trout and cutthroat trout are naturally found together only in the Kootenai River drainage of extreme Northwestern Montana. Rainbow-cutthroat hybrids represent a serious threat to native populations of unhybridized cutthroat trout. Hybrid trout will interbreed with native trout and all of the resulting offspring are hybrid trout with non-native genetic material.

Contributors: Matthew Corsi

Glossary:
  • Hybridize
    the interbreeding of two different species.
References:
  • Allendorf et al. Intercrosses and the U.S. Endangered Species Act: should hybridized populations be included as westlsope cutthroat trout? 2004. Conservation Biology.
  • Downs et al. Age at sexual maturity, sex ratio, fecundity, and longevity of isolated headwater populations of westslope cutthroat trout. 1995. North American Journal of Fisheries Management.