Histological features of atretic stages of the ovarian follicles of two viviparous teleost species: Ilyodon whitei (Meek, 1904) and Goodea atripinnis (Jordan, 1880) (Goodeidae)

Abstract

Atresia, the process of degeneration and removal of ovarian follicles from the ovary is an essential aspect of the ovarian physiology. It plays an important role in fecundity, reducing the number of maturing oocytes. In viviparous teleosts, atresia shows special characteristics because of the dual reproductive role of the ovary, as the place for follicular development and gestation. The histological features of atretic follicles in two species of viviparous teleosts, Ilyodon whitei and Goodea atripinnis, were observed. The ovaries were processed histologically. These species have a different average number of embryos, 30 in I. whitei, and 55 in G. atripinnis. All the ovaries observed during non gestation and gestation stages of I. whitei and G. atripinnis contained atretic follicles. Follicles may become atretic at previtellogenic and vitellogenic stages. In both species, late vitellogenic oocytes are seen only around the time of fertilization. All of the non-fertilized vitellogenic oocytes become atretic. In both species, late vitellogenic oocytes were not seen during late gestation, and most of the early vitellogenic oocytes observed were atretic.