Background. European perch, Perca fluviatilis Linnaeus, 1758, is a predatory freshwater fish present also in the coastal waters of the Baltic Sea. The available catch data indicate that the population profile of this species is disrupted, and the condition of the population is not stable. The aim of this study was to determine the diversity and genetic structure of and assess phylogenetic links and gene flow between selected perch populations originating from various types of reservoirs in northern Poland. Materials and methods. A total of 392 perch were collected from selected bodies of water in north-western Poland and the fin samples were preserved in 96% ethanol or stored for short periods at –20°C. Genomic DNA was isolated, while for further mitochondrial DNA analysis, a 1081-bp fragment of the control region was amplified. Amplification products were sequenced and subjected to restriction analysis (PCR-RFLP) in order to determine the genetic diversity of the control region of mtDNA. The obtained sequences were analyzed using bioinformatics tools, and phylogenetic trees were generated to determine the degree of diversity between individuals in selected perch stocks. Results. Seven haplotypes were identified. Ten polymorphic sites were defined, and the degree of genetic diversity between selected haplotypes was determined. Based on the distribution of perch haplotypes, stocks from Pomeranian Bay (haplotypes F, D), the Szczecin Lagoon (haplotypes D, F, H), and the more homogeneous stocks from Pomeranian Bay (haplotypes F, D) and the Kamieński Lagoon (D, F) can be distinguished. Analysis of phylogenetic relations allowed identifying stocks with the most conserved genome, similar to the standard perch genome, and stocks that have become more genetically distant, probably due to the diversity of the inhabited ecosystems or natural hybridization observed in this species. Conclusion. European perch inhabiting waters of north-western Poland is a species with high plasticity, without isolated stocks or populations that can be clearly distinguished on a genetic basis. It does, however, have a tendency for mitochondrial genomic modifications, which is likely due to the broad spectrum of ecosystems inhabited by the species. Due to the homogeneity of the perch populations from the Szczecin Lagoon, the Kamieński Lagoon, and Lake Myśliborskie, they should be used for the restoration of populations in water bodies in which their genetic structure is severely disrupted. For the same reason, the policy of perch catches should be modified. The authors suggest increasing the protected size to 20 cm and limiting the catches of the species as by-catch by modifying fishing tools, including the introduction of a seasonal prohibition of tools that might eliminate individuals of 15–16 cm in length from natural waters in their spawning period.

Percidae, mtDNA, genetic diversity, haplotypes