GENETICALLY MONOMORPHIC BROWN-TROUT (SALMO-TRUTTA L) POPULATIONS, AS REVEALED BY MITOCHONDRIAL-DNA, MULTILOCUS AND SINGLE-LOCUS MINISATELLITE (VNTR) ANALYSES

Normally, populations of brown trout are genetically highly variable. Two adjacent populations from north-west Scotland, which had previousl y been found to be monomorphic for 46 protein-coding loci, were studie d by higher resolution techniques. Analyses of mitochondrial DNA, mult ilocus DNA fingerprints and eight specific minisatellite loci revealed no genetic variation among individuals or genetic differences between the two populations. Continual low effective population sizes or seve re repeated bottlenecks, as a result of low or variable recruitment, p robably explain the atypical absence of genetic variation in these tro ut populations. Growth data do not provide any evidence of a reduction in fitness in trout from these populations.