Ovarian follicular atresia in two teleost species: a histological and ultrastructural study.

Follicular atresia is a common phenomenon in vertebrate ovaries involving the oocyte and the follicular wall degeneration. Female Astyanax bimaculatus lacustris and Leporinus reinhardti were kept in aquaculture cages inside tanks from February 1994 to January 1995 for the study of the characteristics of different stages of follicular atresia. Histological and ultrastructural analysis demonstrated similarities in the degenerative events and in the resorption of oocytes in both species. Degradation of organelles, such as mitochondria, cortical alveoli, and annulate lamellae occurred in the peripheral ooplasm during the initial stage of the process. Follicle cells showed marked phagocytic activity with digestive vacuoles, myelin figures, and lipofuscin granules during the intermediate and advanced stages of follicular atresia. Granulocytes were in activity during the final stage of follicle resorption. The duration of follicular atresia was 4 months in Leporinus reinhardti and 7 months in Astyanax bimaculatus lacustris. When submitted to induced reproduction in December 1995, 50-60% of the females of both species responded to induced spawning, indicating the recovery of gonadal activity. It is suggested that, in captive conditions, follicular atresia is shorter in total-spawning fishes when compared to those showing partial spawning, and that it has no apparent deleterious effects on induced reproduction in the subsequent cycle.