Abstract
A comparative study of disturbed (downstream) and undisturbed (upstream) populations in a French Mediterranean river (the Sorgue) was conducted to assess the fate of introgressing hatchery-genes in the aboriginal gene pool. Variation was assessed at 27 protein-coding loci, three microsatellite loci and two mtDNA restriction sites. The results were compared to those from another Mediterranean drainage basin (that of the river Orb). The genetic pattern observed among markers and drainage basins was found to be noticeably different. A reduction in population size is hypothesized to explain the lower 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.