Natural and domestic introgressions in the marble trout population of Soa River (Slovenia)

The endemic marble trout, Salmo trutta marmoratus, suffered massive stocking with brown trout in Slovenia and Italy. In the Soa River (Slovenia) long-term surveys have evidenced Danubian and Atlantic introgressions. The observation of discrepancies between introgression frequencies when using morphology, mitochondrial sequences, allozymes, or microsatellites markers led to reanalyze the hybrid population of the Soa River. New analyses on diachronic samples of the Soa hybrid populations was performed, genotyping partly the same individuals on one diagnostic allozyme (LDH-C1*), eight microsatellite, and one mitochondrial loci. The confirmed discrepancies led to interpret the anomaly as the consequence of ancient natural immigration of Danubian trout by rivers captures together with stocking with Atlantic domestic trout. Management consequences are discussed because the natural Soa inhabitant which was thought to be a pure marble trout should be now changed into a natural hybrid lineage accepting few Danubian alleles.