Mystus nigriceps commonly inhabit the Tarai River that has been polluted and it may affects the reproductive biology of the fish. A study aims to understand the reproductive biology of M. nigriceps has been conducted. The fish was sampled 5 times, once/two weeks, from April to July 2019. Parameters measured were Sex Ratio, Gonad maturity Level, Gonad Somatic Index (GSI), fecundity and egg diame…