Investigations on Some Aspects of Reproductive Biology in

Abstract: The present study was carried out to investigate some aspects of the reproductive biology of Oreochromis niloticus inhabited Abu-Zabal Lake to mange this species in this newly man made lake. Size at first maturity, gonado-somatic index (GSI), hepato-somatic index (HSI), egg diameter and fecundity were studied. Moreover, histological examination of the ovary was performed. At the first sexual maturity (L), the50 body length of females O.niloticus was smaller than males (10.5 and 11.5 cm, respectively). The breeding period (G.S.I.) of females extended from March to September. Fecundity variation was better correlated with length (r = 0.9236) and weight (r = 0.9399) than with gonadal weight(r = 0.7651). Fecundity ranged between 289-1456 eggs corresponding to fish total length of 10-23 cm with an egg diameter ranged from 1.99-2.45 mm. The histological findings support the biological results which elucidated that the spawning season of O.niloticus extended from March to September. The development of oocyte during spring go with the secondary growth phase (vitellogenic oocyte), while the development during summer and autumn were found in the primary growth stage (early and late perinucleolus and yolk nucleus stages). In winter, development of oocytes in the secondary growth phase (tertiary yolk stage) was in the artetic form. It was concluded that, it is essential to increase the mesh size used in Abu-Zabal lakes to catch O.niloticus to lengths greater than 12.0 cm to protect this species from exploitation. Key words: Reproductive biology Oreochromis niloticus Gonadosomatic index Hepatosomatic inde