Development and fate of the postovulatory follicle complex, postovulatory follicle, and observations on folliculogenesis and oocyte atresia in ovulated common snook, Centropomus undecimalis (Bloch, 1792)

Abstract

The common snook, Centropomus undecimalis, was induced to ovulate using a time-release, GnRH analogue. Ovulation occurred the afternoon or evening the day after hormone administration. The time of ovulation was established within half an hour. At ovulation, three fish per time-group were divided into 0, 6, 12, 18 hr and one thru five days post-ovulation to study changes in the postovulatory follicle complex (POC). Histology of the ovaries revealed changes in the POC, postovulatory follicle (POF) and oocyte atresia through five days post-ovulation. Within 24 hr, nuclei of the POF cells lost their initial spherical or oval configuration, and by four days the basement membrane within the POC had fragmented. There was a temporal separation between ovulation and post-ovulation folliculogenesis; that is, in that the formation of new follicles commenced within the germinal epithelium between 12–48 hrs after ovulation. Morphology of the POC was best revealed with the reticulin stain; it is composed of the POF and postovulatory theca (POT). These are separated by a basement membrane, reflecting the origin of a follicle from a germinal epithelium while the theca is derived from stroma. The POF is composed of the former follicle cells that surrounded and contacted the oocyte during its development; the follicle is composed of the oocyte and its surrounding follicle cells. The POC is composed of a prominent basement membrane separating the POT from the POF. The reticulin stain clearly defines compartmentation in the ovary and supports redefinition of the POF as the follicle cells that formerly surrounded the oocyte prior to ovulation. J. Morphol. 278:547–562, 2017. © 2017 Wiley Periodicals, Inc.