Sexual dimorphism and microanatomical parameters of the Black sea sprat Clupeonella cultriventris (Nordmann, 1840) of the Bug lagoon during its spawning migration

Purpose. To analyze sexual dimorphism of the Black Sea sprat Clupeonella cultriventris (Nordmann, 1840) of the Bug lagoon under current conditions. To study the dynamics of changes in mesonephros structure during spawning migration from the estuary to the Southern Bug River. To determine the prospect of using the data of histological monitoring in ichthyological practice for the assessment of fish morphofunctional status. Methodology. Primary materials were obtained during scientific and commercial fishery surveys carried out in the Dnieper-Bug estuary system. Control stations were located along the spawning migration pathways of the Black Sea sprat from the Bug lagoon to the South Bug River. Field and laboratory processing of ichthyological samples was performed according to generally accepted methods and guidelines. Histological studies were performed using author’s equipment and original methods specially intended for fish tissue diagnostics. Findings. The studies indicated on the presence of a significant sexual dimorphism in the Black Sea sprat Clupeonella cultriventris (Nordmann, 1840) of the Bug lagoon. The comparative analysis of twenty-four plastic features showed that sprat females had a higher body depth (td=6.11; р<0.05), shorter body (td=8.62; р<0.05)and caudal peduncle (td=7.64; р<0.05). Females also had the displacement of fins in the caudal direction that that was manifested as a significant difference between antedorsal, antepectral, anteventral, anteanal, pectoventral, and ventroanal distances (td=4.39-9.67; р<0.05). Linear parameters of fins (length, height) also differed significantly (td=3.96-11.23; р<0.05). It is important to mention that these features in females were larger than those in males. An exception was the anal fin height, which was significantly higher in males than in females (td=6.85; р<0.05). No differences were detected for abdominal fin length (td=0.03; р<0.05) that was also typical for head length (td=0.15; р<0.05). No significant differences were detected in the head area. A significant differences was observed only for eye diameter and postorbital distance (td=4.15-7.99; р