Atresia of oocytes for northern rock sole Lepidopsetta polyxystra (Pleuronectiformes, Pleuronectidae) from the Pacific waters of Kamchatka

Abstract

Northern rock sole is abundant and important for fishery species in the Pacific waters of Kamchatka and northern Kuril Islands. Sometimes its oogenesis occurs with the oocytes atresia. By the data of the females reproductive tissue investigation conducted in 2011-2012, the degeneration appears for the late perinucleus (II and II-III maturing stages), vitellogene cells (III and IV stages), and ovarian follicles (stages VI-III) and develops by three principally different ways. Comparing with other fish species, atresia of the late perinucleus of northern rock sole realizes without follicular epithelium and affects either 15 % of these cells (for 8 % of juveniles) or 67 % of these cells (for 4 % of non-spawning adults). In the process of the vitellogene oocytes atresia, a symplast forms between follicular epithelium and chorion and conserves until final resorption of the oocyte. The cortical alveoli and vacuolated cells are damaged more often (5.6 %) than the oocytes with advanced yolk (2.4 %). Resorption of ovarian follicles by stroma connective tissue of oviparous plates is typical for all postspawning females, their portion doesn’t exceed 3 % of cells in each generation. Obviously, atresia of vitellogene oocytes reduces the fish fecundity, therefore the total and population fecundity is forming until the stage IV.