Mugil cephalus L. in Negombo lagoon (7°10’N and 79°50’E), Sri Lanka, were observed to be non-intermittent spawners who spawn once during their spawning season, which extends from October to November. In small length groups, males were more abundant by a 1:1 sex ratio was attained with growth. The mean lengths at maturity were 33.7 cm and 37.0 cm for males and females respectively. The fecundity ranged from 0.71 x 106 to 1.7 x 106 for fish ranging in size from 34 cm to 46 cm. The relative gut length, which varied from 3.52 to 5.14, did not change significantly with size. The main food item of the fish above 10 cm in total length was serpulid polychaetes. Composition of the diet did not change significantly with growth.