Allozymes, mtDNA and microsatellites study introgression in a stocked trout population in France

A comparative study of disturbed (downstream) and undisturbed (upstream) po pulations in a French Mediterranean river (the Sorgue) was conducted to ass ess the fate of introgressing hatchery-genes in the aboriginal gene pool. V ariation was assessed at 27 protein-coding loci, three microsatellite loci and two mtDNA restriction sites. The results were compared to those from an other Mediterranean drainage basin (that of the river Orb). The genetic pat tern observed among markers and drainage basins was found to be noticeably different. A reduction in population size is hypothesized to explain the lo wer variability observed in the upper part of the river Sorgue. Estimations of hatchery gene flow were different between loci but in the same range of values between markers.