Success of Basibranchial Teeth in Indicating Pure Populations of Rainbow Trout and Failure to Indicate Pure Populations of Westslope Cutthroat Trout

Abstract

Horizontal starch gel electrophoretic analysis of proteins was used to determine whether fish in the 19 trout populations sampled were pure westslope cutthroat trout Onchorhynchus clarki lewisi, pure rainbow (redhand) trout O. mykiss or hybrids of these fishes. The presence or absence of basibranchial teeth was also determined for the fish in the samples. High proportions of fish with basibranchial teeth were found among samples of both pure and moderately hybridized westslope cutthroat trout populations, making this attribute an unreliable indicator of hybridization for samples from the Clark Fork River drainage, Montana. Basibranchial teeth were absent in all pure rainbow trout sampled from populations native to tributaries of the Kootenai River, Montana. It appears that the absence of basibranchial teeth is a reliable indicator of pure rainbow trout populations in this drainage. In contrast, basibranchial teeth were present in at least one fish in each sample of rainbow trout that showed some hybridization with westslope cutthroat trout. The presence of basibranchial teeth in rainbow trout, therefore, appears to be a reliable indictor of hybridization between rainbow trout and westslope cutthroat trout in the Kootenai River drainage.