Ultrastructural study of the gonadal development of the cichlid fish, Cichlasoma dimerus (Heckel, 1840)(Teleostei, Perciformes).

F. J. MEIJIDE F. L. LO NOSTRO; M. PANDOLFI AND G. A. GUERRERO

La Paz, México.

Congreso; 2000 Joint Annual Meeting of the ASIH, AES, NIA, HL, CAH and SSAR; 2000

Universidad Autónoma de Baja California Sur

In the present study, gonads from larval and juvenile stages of Cichlasoma dimerus are analized at the ultrastructural level. C. dimerus, a perciform teleost, is classified as a differentiated gonochorist (Yamamoto, 1969), 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 three pairs of adult fishes captured in Esteros del Riachuelo (Corrientes, Argentina). They were kept in 15 l 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. Samples were fixed in 3% glutaraldehyde in 0,1M phosphate buffer (pH 7,4) for 4 hours, and postfixed in 1% osmium tetroxide for 2 hours. Semithin sections stained with toluidine blue were used for orientation. The ultrastructure of the germinal epithelium and interstitial components is described, both in the undifferentiated and differentiated gonads. This basic research is a necessary first step for further studies on the effect of xenobiotics on the gonadal sex differentiation.