“Development of the ovarian germinal epithelium in the cichlid fish, Cichlasoma dimerus (Teleostei, Perciformes)”.

F. MEIJIDE; F. LO NOSTRO; G. GUERRERO

Manaos, Brasil

Congreso; 81th Annual Meeting American Society of Ichthyologist and Herpetologits (ASIH-AES).; 2003

The source of oocytes and follicle cells that compose the ovarian follicle in adult teleosts is the ovarian germinal epithelium, but the process has been documented only in a few species. Likewise, the ontogenetic development of stromal elements that surround teleost follicles has not been adequately addressed. Studies conducted using paraffin embedment for ovarian histology obscured histological relationships. The problem with studying the origin of ovarian follicles is that the cellular detail required for adequate description is not resolvable with paraffin techniques for light microscopy. Only electron microscopy provides the necessary resolution and detail to properly describe the formation of follicles and surrounding stromal tissue. Spatial relationships between cellular elements and the basement membrane must be taken into account when studying the origin of follicles and the ovarian stroma. In this work, we studied the process of folliculogenesis during early ontogenesis. Gonads from larval and juvenile stages of Cichlasoma dimerus were examined at the ultrastructural level. C. dimerus, a perciform teleost, is classified as a differentiated gonochorist, in which an indifferent gonad develops directly into a testis or ovary. This freshwater species adapts easily to captivity and spawns with high frequency during eight months of the year, representing an appropriate model for developmental studies. Larvae were obtained from natural spawns of six pairs and kept in aquaria at 26,5 ± 1 ºC and 12:12 hours photoperiod. Gonadal tissue from larvae and juveniles between 15 and 90 days post-fertilization, covering the period of histollogically evidenced sex differentiation, were processed according to TEM techniques. Semithin sections stained with toluidine blue were used for orientation. The development of the ovarian germinal epithelium is described. The follicle is a derivative of the germinal epithelium, the epithelial cells of which originate from the coelomic epithelium. Each follicle is composed of an oocyte and surrounding follicle cells. It is separated from the encompassing theca by a basement membrane. Epithelial cells transform into follicle cells during folliculogenesis. Thecal cells seem to be derived from the subepithelial connective tissue