Reproductive Cycle of the Endangered Pabda, Ompok pabda (Hamilton-Bouchanan, 1822) in Bangladesh

Successive developmental stages of both male and female gonads and estimation of gonado-somatic index (GSI) of Ompok pabda (Hamilton-Bouchanan, 1822) belonging to family Siluridae were investigated over a two year period (November 2005 to October 2006). From thehistological analysis, four developmental stages namely; spermatogonia, spermatocytes, spermatids and spermatozoa were identified in testes. Three developmental stages of oocytes: ogenesis (oogonia, early perinucleolus stage and late early perinucleolus stage), vitellogenesis (early vitellogenic oocytes, advanced vitellogenic oocytes and maturation stage) and atretic stages were distinguished in ovaries. Maximum mean gonad weight was recorded in June for both females (9.05±0.72 g) and males (2.39±0.28 g). The testes at early development stages between November and March contained mostly spermatogonia, spermatocytes and spermatids, although a small amount of spermatozoa was also found in late March. The mature testes began to develop in early April and were prominent from May to July. Highest percentage of oogonia in the ovary was recorded in the month of December; while highest percentage of early perinucleolus stage and late perinucleolus stage were recorded in the month of January. Vitellogenesis (matured oocytes) occupied the most areas of the ovaries which were observed from May to July but it was prominent in June. The oocytes did not mature at the same time. Only the matured oocytes ovulated during the spawning period while immature oocytes gained maturation under way of vitellogenesis and released at the second spawning time.