GENETIC INTROGRESSION BETWEEN NATIVE AND INTRODUCED BROWN TROUT SALMO-TRUTTA L POPULATIONS IN THE RHONE RIVER BASIN

In the Doubs River (Rhone drainage) two distinct brown trout (S. trutt a) phenotypes are observed. One phenotype is locally called Doubs trou t and is characterized by four black stripes on the sides, similar to perch (Perca fluviatilis L.) and the other is the common phenotype of the fluviatile ecotype of brown trout, Salmo trutta f. fario. Protein data for three samples from the Doubs show that the Doubs trout belong s to the Mediterranean population group of brown trout, whereas the fa rio phenotype originates from stocking with hatchery strains of Atlant ic basin origin. The two forms, however, do not hybridize freely. This is indicated by considerable gametic phase disequilibrium between all eles of hatchery and Doubs trout at one sampling site, and by lack of intermediate genotypes and phenotypes at another sampling site. The in trogression patterns observed at the two sites suggest that difference s in local habitat conditions can affect the degree of hybridization a nd introgression.