ABSTRACT
The present work was carried out using twenty mature Epinephelus tauvina [Perciforms: Serranidae] collected from Arabian Gulf coast at Dammam City. Fishes of this species are known to undergo sex change during certain stage of their life cycle. Histological and enzyme histochemical studies were performed on gonads of the collected fishes. The examination of the gonads of E. tauvina revealed the presence of three developmental phases during the sex change process. These were: Female, early transition phase and late transition phase each one may subdivide into two stages. In female phase several developmental stages of the oocytes were recognized. At the beginning of early transition phase perinucleolar mature oocytes began degeneration while late transition phase characterized by rapid proliferation of spermatogenic cells. The histochemical studies demonstrated that alkaline phosphatase enzyme gave intense reaction in granulosa cells of mature oocytes while acid phosphatase gave an intense reaction in the interstitial cells and atretic follicles but delta S -3 beta hydroxysteroid dehydrogenase enzyme gave intense reaction to special cells in capsule of gonads