Gonad Differentiation and Early Gonadal Development of the European Eel Anguilla anguilla L. in Egyptian Waters PDF

Keywords

gonadal development, freshwater European eel, Sex differentiation

Abstract

Sex differentiation and gonadal development in the freshwater European eel, Anguilla anguilla L. was histologically studied for elvers, young 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 destined 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 gonads occur at a length of 32.0-35.0 cm. The ovary is the main gonad that directly develops, while the testis plays the role of secondary sex development. The oocytes proliferate rapidly, but the testis enters a period of quiescence. Both sexes posses gonads in immature conditions, the oocytes at the previtellogenic stage and spermatogonia in late multiplication stage. The presence of a vas deferens during gonadal development signals testicular differentiation, and its absence leads to ovarian development.