GONAD DIFFERENTIATION AND EARLY GONADAL DEVELOPMENT OF THE EUROPEAN EEL ANGUILLA-ANGUILLA L IN EGYPTIAN WATERS

Sex differentiation and gonadal development in the fresh water Europea n eel. Anguilla anguilla L. was histologically studied for elvers, you ng and adults. The sex groups were divided into undifferentiated elver and adult and definite female or male. The successive examinations of the eel's gonads revealed that the primordial germ cells first appear in 6.4-10.0 cm elvers and the oogonia in 15.0 cm ones. Elvers destine d to become females differentiate sexually at a length beyond 19.0 cm and those destined to become males beyond 27.0 cm, but some adult fish 38.0 cm in length still have undifferentiated gonads. Hermaphrodite g onads occur at a length of 32.0-35.0 cm. The ovary is the main gonad t hat directly develops, while the testis plays the role of secondary se x development. The oocytes proliferate rapidly, but the testis enters a period of quiescence. Both sexes possess gonads in immature conditio ns, the oocytes at the previtellogenic stage and spermatogonia in late multiplication stage. The presence of a vas deferens during gonadal d evelopment signals testicular differentiation, and its absence leads t o ovarian development.