Various biological aspects of a sciaenid, Johnius macrorhynus, exploited off Mumbai are reported. The length-weight relationship was found to be Log W=-5.18 + 3.12 Log L. Crustaceans, dominated by Aretes spp. constituted the main food in the smaller fishes. However, the adult and larger fishes fed on prawns and fishes. Size at first maturity was calculated as 219.5 mm. The species was found to spawn in two seasons. Fecundity ranged from 87,935 to 1, 01,539 eggs per 100 g body weight.