Abstract

This study was conducted to observe the month-wise gonado-somatic index (GSI), identify breeding frequency, peak breeding season, process of gametogenesis and furnish guideline for conservation of a threatened fish species Mystus cavasius from the ‘Haor’ region in the Northeaster Bangladesh. The GSI of male M. cavasius was found highest (3.41) in early July and the lowest (0.05) in late September and for female it was highest (24.54) in late July and the lowest (0.19) in October. Presence of oogonia (OG), perinucleolar oocyte (PNO), previtellogenic oocyte (PVO), yolk vesicle (YV), yolk granule (YG), premature (PM) and mature (M) stages of oocytes observed in the histological study of ovary. The mature stages of oocytes (PM and M) were observed in early July to August samples and developed oocytes (OG, PVO and PNO) were observed in the September samples. It was found that oocytes did not develop synchronously. Spermatocytes (SPC), spermatids (SPT) and spermatozoa (SPZ) testicular germ cells were identified during July to October samples. High proportions of mature germ cells (SPT and SPZ) were observed during July to August samples of testes when SPC was in low proportions. In post-monsoon samples (September to October), high abundance of early stage germ cells (mainly SPC) were observed indicating spent phase of testes. The study indicated that the peak breeding season of M. Cavasiusto be July owing to occurrence of high GSI and appearance of mature oocytes and mature testicular germ cells in this month. This study provides the first detailed information about oogenesis and spermatogenesis of M. cavasius from the Mymensingh Region of Bangladesh.

Keywords: Mystus cavasius; Gametogenesis; Gonadosomatic index; Haor basin