AGE PECULIARITIES AND SEASONAL DYNAMICS OF HAMETOGENESIS IN POPULATIONS OF ESPERIANA ESPERI (GASTROPODA, PECTINIBRANCHIA, MELANOPSIDAE) OF UKRAINE

Article are presents the results of features of gametogenesis and its seasonal dynamics in Esperiana esperi (Ferussac, 1823). In Ukraine, these rheophilic mollusks are common in the coastal stretches of large rivers that form part of the hydroelectric network of its Right Bank. The populations of these animals belong to the category of polycyclic, that is, consisting of individuals of several generations, with a maximum life expectancy of about two years. The study found that gametogenesis in E. esperi is a synchronous process that occurs under the same environmental conditions during spermatogenesis and ovogenesis. Examination of the histological sections of the sex glands of these mollusks revealed that it is a stage process that involves five stages of maturity of the gonads: the beginning of gametogenesis, active gametogenesis, pre-spawning, spawning and post-spawning stages, which are characteristic for certain seasons of the year. According to the analysis, there is a direct correlation between the stages of gametogenesis and the temperature conditions of the environment. Accordingly, gametogenesis in southern mollusk populations has been found to occur earlier than northern populations. The number of mature oocytes determines the time of occurrence of fertility peaks, which occur mainly in July for northern populations and for June for the same southern populations of molluscs, indicating a different temperature optimum. According to the latter, the highest levels of stability are characterized by southern populations of the species studied. Generalized information on the number of oocytes also characterizes the duration of periods of E. esperi life cycles from the northern and southern territories of the habitat in Ukraine under current climatic conditions. These molluscs are found to have the longest reproduction period, which lasts about a year. Reproduction takes only 3.5 months, and post-reproduction takes 1-3 (as an extreme rarity - up to 7 months in northern populations).