The genetic diversity of native, stocked and hybrid populations of marble trout in the Soca river, Slovenia

The marble trout (Salmo marmoratus) is an endangered species in Slovenia la nd in Italy, Croatia and Albania) because of hybridization resulting from i ntensive stocking. Eleven populations of trout from the Soca river basin (S lovenia) were analysed using 31 presumptive enzyme loci. Three European con trol samples representing the main European genotypes of brown trout were a lso analysed. This analysis confirmed the existence of extensive hybridizat ion in the main river, resulting in an equal mixture of alleles belonging t o marble trout, and Danubian and Atlantic brown trout (Salmo trutta). Despi te the high level of introgression observed in the main Soca River, nearly pure populations of marble trout were found in the headwaters of five tribu taries. The five stations with pure marble trout will be the basis of a reh abilitation programme. Hardy-Weinberg and linkage disequilibria were observ ed and hypotheses are discussed to explain this. A scenario for the coloniz ation of the Adriatic region is proposed.