Genetic variation among trout in the River Neretva basin, Bosnia and Herzegovina

Mitochondrial DNA haplotypes, characteristic of the Adriatic, Danubian and Atlantic lineages of brown trout Salmo trutta and of Salmo obtusirostris were found in trout inhabiting the River Neretva basin. With the exception of the one associated with softmouth trout, haplotypes were not correlated with operational taxonomic units based on phenotype. Nuclear DNA analysis identified four genetic assemblages corresponding to S. obtusirostris , different geographically confined autochthonous S. trutta populations, introduced S. trutta and a genetically heterogeneous group located between S. obtusirostris and S. trutta in the dendrogram of individuals, indicating the existence of hybrid swarms in the Neretva basin. Genetic assemblages corresponding to Salmo marmoratus and the recently proposed Salmo cf. montenigrinus were not detected. The presence of genetic intermediates indicates that the studied taxa are not completely reproductively isolated and that genetic stability has been either anthropogenically interrupted or not yet achieved among Neretva trout. This finding should be considered in management decisions since such an unstable community must be particularly susceptible to breakdown in genetic population structure as a result of hybridization between native and non-native introduced trout stocks.