Genetic evidence for limited introgression between wild and stocked individuals in Portuguese brown trout, Salmo trutta, populations

The level of introgression between wild and stocked individuals in Portuguese Salmo trutta populations was evaluated. Fish were sampled from rivers of the Douro Basin and compared with fish used in restocking programme. This study, based on microsatellite and allozyme loci, showed, thanks to the most discriminant loci, a low percentage of heterozygote individuals. This happened due to absence or low levels of intercrossing between stocked and native brown trouts. Stocking practices in Portugal are inefficient, as suggested by mtDNA haplotype distribution. New policies for stocking and monitoring hatchery fish are needed to preserve the gene pools of wild Portuguese trout populations.