Minimal gene flow from introduced brown trout (Salmo trutta L.) after 30 years of stocking

Abstract

Summary Lake Tinnsjo, Norway, has been heavily stocked over three decades with two different brown trout stocks. A population genetic survey based on 13 allozyme coding loci was conducted to investigate the genetic composition of the present trout population and the genetic impact of the two donors. Contrary to expectations, highly significant differences in allelic frequencies between Lake Tinnsjo trout and the two donor stocks were found at several loci, suggesting minimal gene flow from stocked trout to the wild populations. Pairwise genetic distance values were several times higher between donor stocks and Lake Tinnsjo samples than between the various spawning inlets to Lake Tinnsjo. Fst increased from 0.024 to 0.090, when samples from the donor stocks were included in the material. There were no deviations from expected Hardy–Weinberg distribution of genotypes in the spawning inlets. It was concluded that the donor stocks contributed little to the trout gene pool in the lake. A possible exception is the trout population below the lake outlet.