BIOLOGICAL FEATURES OF TARAN (RUTILUS HECKELII) OF THE DNIEPER-BUG ESTUARY SYSTEM

Purpose. To analyze morphological variability and basic biological features of the modern stock of taran of the Dnieper-Bug estuary system in the conditions of the transformed Dnieper flow. Methodology. Morphological variability was determined based on the comparison of morphological features of roach Rutilus rutilus (Linnaeus, 1758) of the Kakhovka reservoir and semi-migratory taran Rutilus rutilus heckelii (Nordmann, 1840) of the Dnieper-Bug estuary system. As a main criterion of the evaluation of the taran stock biological state, we used age, sex structure, growth characteristics, fecundity and condition factor. Fish sampling was carried out at stationary monitoring-observation stations of the Institute of Fisheries NAAS of Ukraine. Field and cameral processing of the collected materials were performed based on conventional methods and guidelines. Findings. Morphological variability analysis demonstrated significant differences between Dnieper and Bug taran. The highest differences were observed for antroventral distance (td=11.19). Significant differences were also observed for antenanal and ventroanal distances td=4.05-4.14. No significant differences were found for meristic features. There were also significant differences between Dnieper-Bug taran and Kakhovka reservoir roach, which had formed a resident form after regulating the Dnieper River flow. Kakhovka reservoir roach is more deep-bodied with Н=32.79%, t-test value was 5.65. Pelvic fins were more shifted to the caudal fin (td=5.28) that resulted in significant difference (p<0.05) in ventroanal distance (td=4.26). Taran also had somewhat smaller length of the anal fin base (td=4.73) but its height was higher ? td=5.78. The main peculiarity of the current biological state of taran stock is the domination of young age groups. The small number of fish in the boundary groups of the age series right wing with relative stability of growth features indicate on intensive pressure on the commercial stock recruitment. Originality. For the first time in recent years, we performed a comparative analysis of plastic and meristic features of taran of the Dnieper-Bug estuary system. The information on age, sexual structure and length-weight growth of the taran stock was significantly updated and supplemented. Practical value. The obtained values are a scientific basis for optimizing commercial fishing pressure on fish fauna of the Dnieper-Bug estuary system, which is important in the regard of biodiversity conservation in the natural water bodies of Ukraine.