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¹ University of Rajshahi, Department of Genetic Engineering and Biotechnology, Rajshahi-6205, Bangladesh DOI : 10.4194/1303-2712-v17_3_15 Viewed : 3926 - Downloaded : 4049 The present study was the detailed investigation to identify maturity of female Mystus tengara in the Ganges River of Rajshahi (24°22´N; 88°35´ E), northwestern Bangladesh. Specimens (n = 921) were collected monthly from January to December 2015, using cast nets (mesh size = 17 mm) for adults and purse-seine and trap nets (mesh size = 4 mm) for juveniles. Histological analyses of 171 females were performed in which oocyte development was divided into five stages, with the oocyte size range from 33 to 1609 µm in diameter. The ovarian cycle of Mystus tengara was divided into three periods: a long period of early oogenesis (emerging from December but expands to April as the initiation time of early oogenesis for all the oocytes were not similar), a short period of vitellogenesis (February to April) and a spawning period from May through July with peak activity in June. Both gonadosomatic (I_G) (up to 16.2%) and hepatosomatic indices (I_H) (up to 3.7%) can be used together to predict the spawning period where the females were observed to spawn in June and July. Total lengths at minimal observed maturity/50% maturity (L_T50)/95% maturity (L_T95) values were 7.9/8.9/11.1 cm for females. Mystus tengara is likely an asynchronous multiple spawner with indeterminate fecundity . Keywords : Oocyte, sexual maturity, vitellogenesis, asynchronous, indeterminate fecundity