Brown Trout-Salmon Hybrids in Bulgarian Rivers are not a Red Herring

Brown trout (Salmo trutta fario) is a popular object of recreational fishing in Bulgaria and throughout Europe. Free-living ('wild') populations of brown trout are seen in many cold water rivers, and restocking of artificial as well natural water basins is carried out routinely. Genetic analysis for a microsatellite marker common for several salmonid species but discriminative in regards to species affiliation shows that allele lengths uncharacteristic of brown trout but typical of Atlantic salmon may be observed in Bulgarian 'wild' populations of brown trout. It is possible that a subpopulation containing interspecies hybrids with Atlantic salmon exists in the Bulgarian water basins populated with brown trout. Since brown trout-salmon hybrids have been shown to be viable and fertile, the possibility for future interspecies introgression cannot be ruled out. The biodiversity of Bulgarian natural populations of salmonid fishes may benefit from a more finely tailored stocking strategy.