Dominant Meristic Traits of Fish and Their Association with Habitat Water Quality Parameters: A Case Study

Fish morphological traits are increasingly recognized as sensitive bioindicators of aquatic ecosystem quality. This study investigated the associations between dominant meristic traits, which are a subset of morphological features of six common freshwater species, Alburnus alburnus, Perca fluviatilis, Abramis brama, Rutilus rutilus, Scardinius erythrophthalmus, and Carassius carassius, and chemical parameters of water in the regulated ecosystem of the Styr River, Ukraine. Water quality was evaluated using biochemical oxygen demand (BOD5), chemical oxygen demand (COD), dissolved oxygen (DO), nutrients, solids, pH, and water quality classes (WQC). Meristic traits of fish were analyzed through frequency analysis of species (FAS) and the Zakharov scoring method (ZSM), while hierarchical cluster analysis (HCA) and neural networks (NN) were applied to detect associations between meristic traits of fish and water chemical parameters. Results revealed that overall water quality corresponded to WQC I–II (clean to moderately polluted), although COD consistently exceeded permissible limits. Key meristic traits, including fin rays, scales, and gill rakers, showed significant sensitivity to environmental variability, with species-specific responses reflecting ecological adaptation. The integrative use of WQC, FAS, ZSM, HCA, and NN demonstrated the potential of meristic traits to serve as reliable indicators of ecological integrity in freshwater systems.