Histological Analysis of Ovarian Development and Sex Ratio of a Catfish, Ompok pabda

A histological analysis of ovarian development as well as the spawning pattern and the sex ratio were determined in an endangered freshwater catfish, Ompok pabda (Hamilton-Buchanan, 1822). A total of 77 fish samples were randomly collected from the same rearing pond for 9 months at the Freshwater Station, Bangladesh Fisheries Research Institute (BFRI), Mymensingh, Bangladesh. The sex ratio of the 77 sampled fish was 40:37 (male:female) and this difference was not significant (p 0.05). From histological analysis, five developmental stages of oocytes were distinguished, namely, (1) oogonia, (2) pre-vitellogenic oocytes including early perinucleolus and late perinucleolus, (3) vitellogenic oocytes including initial vitellogenic oocytes (cortical alveoli) and active vitellogenic oocytes (yolk granules), (4) mature oocytes, and (5) atretic oocytes. The percent distribution of matured oocytes (about 76%), as well as gonado-somatic index (13.73±0.95), were observed to be highest in July, whereas the highest values of both body weight (28.55±2.9 g) and ovary weight (3.85±0.8 g) were recorded in June. Oocytes became larger from April to June (211 μm–295.20 μm) but shrank slightly in July (287 μm). It is evident that O. pabda spawns once a year extending from May to July with the peak spawning period occurring in June and July.