Influence of Migrations of Some Fish Species from the Azov–Black Sea Basin on Their Invasion by the Nematode Hysterothylacium aduncum in Different Seasons

This paper analyzes the influence of prespawning and postspawning planktonophagous and ichthyophagous fish migrations on the degree of invasion by the nematode Hysterothylacium aduncum (Rudolphi, 1802) in the northern parts of the Azov–Black Sea basin. A decrease in the parameters of invasion by an adult nematode in Pontic shad during its wintering in the Black Sea compared to these indicators during its migration after spawning in the Azov Sea has been recorded for the first time. According to the authors, the main reason for the difference in the invasion rate of migrating planktonophagous and ichthyophagous fishes is their transition to new diet. The authors consider that one of the indirect reasons for the differences in the invasion rates of migrating fishes is the unequal salinity in different water areas of the northern parts of the Black and Azov seas.