CHANGES IN THE GENETIC STRUCTURE OF BROWN TROUT (Salmo trutta Linnaeus, 1758) CAUSED BY INTENSIVE STOCKING INTHE UPPER COURSE OF THE NERETVA RIVER
Клучни зборови:
brown trout; genetic introgression; stocking; Adriatic lineage.Апстракт
Brown trout (Salmo trutta Linnaeus, 1758) populations in Mediterranean river systems are characterized by high genetic structuring and local adaptation, making them particularly vulnerable to anthropogenic disturbance. This study assessed changes in the genetic structure of brown trout populations in the upper course of the Neretva River (Adriatic basin, Bosnia and Herzegovina) in relation to long-term stocking practices. Wild riverine populations were sampled at four natural sites and analyzed using mitochondrial DNA control-region markers and a nuclear LDH-C1 locus, complemented by morphometric and meristic analyses. Molecular results revealed a high proportion of autochthonous Adriatic-lineage individuals (≈90%) at all sites, indicating that native genetic integrity is still largely preserved. However, the consistent presence of Adriatic–Atlantic hybrid genotypes (≈10%) across all localities provides clear evidence of introgression from non-native lineages, most likely resulting from historical, non-selective stocking. Morphometric traits showed extensive overlap between genetic groups and proved unreliable for discriminating native and non-native individuals in wild populations, reflecting strong phenotypic plasticity. In contrast, selected meristic traits, particularly the ratio of red to black lateral spots, demonstrated meaningful diagnostic potential when combined with genetic data. Overall, the findings highlight both the conservation value and the genetic vulnerability of brown trout populations in the upper Neretva River and emphasize the need for genetically informed management, including the cessation of stocking with non-native lineages and the implementation of long-term genetic monitoring.
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