Parasitofauna of commercial fish species of the Northern (Small) Aral Sea

The catastrophic desiccation of the Aral Sea and subsequent hydrological changes have profoundly altered the region's ecosystem, leading to the restructuring of both fish communities and their associated parasite assemblages. Despite these changes, data on the current parasite fauna of fish in the Northern (Small) Aral Sea remain extremely limited. This study provides a comprehensive assessment of metazoan parasites infecting commercial fish species in this region. A total of 424 individuals representing 13 fish species were examined, revealing 18 parasite species belonging to seven taxonomic classes: Digenea, Monopisthocotylea, Polyopisthocotylea, Chromadorea, Cestoda, Ichthyostraca, and Copepoda. Overall prevalence was 50%, with intensity ranging from 1 to 100 specimens and mean abundance ranging from 0.03 to 26.5. The highest prevalence and species richness were recorded in Sander lucioperca (83.7%, five species), Abramis brama (68.9%, three species), and Silurus glanis (65%, five species). Ergasilus briani is reported for the first time in the Aral Sea. Dominant species posing the greatest threat to fish health included Diplostomum spp., Tylodelphys clavata, and Achtheres percarum. Molecular analysis confirmed the phylogenetic placement of six parasite species using 18S rRNA sequences (97.4-100% identity), while COX1 data were available for only one species, indicating intraspecific variability and limited reference sequences for some taxa. Comparative analysis with historical data indicates a sharp reduction in metazoan parasite species richness (from 70 to 18 species), while infection levels in key commercial fish remain high. These findings reflect ongoing ecological restructuring and underscore the need for regular monitoring.