Female reproductive cycle of the Dusky grouper, Epinephelus marginatus (LOWE, 1834) in captivity

Abstract

        The paper shows the characteristics of oogenesis in the dusky grouper, Epinephelus marginatus (LOWE, 1834) under conditions of captivity in the southeastern Adriatic. We found no visible ovarian cytological changes or oocytes growth during annual reproductive cycle from October to May. Oocytes started to develop and grow at the beginning of June, when ambient sea temperatures surpass 20° C. The process of vitellogenesis lasts three months, during which time the oocytes grow from 80 to 500 µm in diameter, reaching the size needed for inducing hormonal spawning. Three groups of cells are present in the ovaries: oogonia, previtellogenic oocytes and oocytes in the process of vitellogenesis. During these three months, there is an ongoing process of where new oocytes develop from primary oogonia and grow up to 20-50 µm, as well as the growth of groups of previtellogenic oocytes up to 50-90 µm, along with the development of a number of morphological changes, of which the most prominent is the fragmentation of nucleoli and their migration towards the periphery of the nucleus.
    We observed a significant percent of oocyte atresia in our broodstock and found this a main problem in the artificial spawning.