Abstract: The 2661 specimens of the striped mullet, Mugil cephalus L., used for this study, were collected from high brackish lagoon in south-west Nigeria for 24 months. The size of the 2661 specimens of M. cephalus used for this study ranged from 1.7-29.5 cm standard length (total length: 1.9-39.0 cm). The sex ratio for M. cephalus was 1:0.53 and this showed a statistically significant (p<0.05) dominance of the males over the females for the size range. The fecundity estimates varied from 635,568-1,520,185 and was positively correlated to the fish length and weight. Oocyte diameter averaged 409.64±40.67 μm and this is indicative of an early stage of gonad maturation of the specimens in the lagoon before final spawning occurred. The GSI indicated that spawning activity occurred from December to May in the open ocean.