Nonnative fishes are responsible for declines and extinction of many fish populations worldwide. In western North America, the introduction of nonnative rainbow trout (Oncorhynchus mykiss) frequently leads to the decline and extinction of native cutthroat trout (O. clarki) populations. These species share a similar ecology in streams, thus they are thought to compete for limited resources. As is common in closely related fish species, cutthroat and rainbow trout are able to interbreed producing fertile hybrid offspring. The competitive abilities of hybrid trout may have strong effects on the invasion of remaining native cutthroat populations. Preliminary results indicate that rainbow trout and first generation hybrids with Yellowstone cutthroat trout (O. c. bouvieri) are better competitors for feeding territories than native Yellowstone cutthroat trout. In addition to behavioral differences, body shape is important to competitive interactions and swimming ability in salmonid fishes. The goal of this proposal is to investigate differences in morphology and swimming abilities between Yellowstone cutthroat trout, rainbow trout, and their hybrids. Parental and hybrid trout will be raised in a common environment to determine the genetic basis of morphology and to determine if nonnative and hybrid trout have a higher sustained swimming ability which could provide a competitive advantage. The broader impact of this research will be to provide a better understanding of the mechanisms by which introduced trout are replacing native trout. This project will support the dissertation research of a doctoral candidate.
