Aspects of the biology of Mormyrus rume (Cuvier and Valenciennes) in Lekki lagoon were investigated. This included the length-weight relationship, condition factor, food and feeding habits and the fecundity of the fish species. The major fishing methods employed for collecting the 225 specimens were castnetting and setnetting. The total lengths ranged from 15.0 to 24.9 cm while the standard lengths ranged from 13.0 to 23.0 cm. The body weights also ranged from 26.2 to 99.3g. The fish exhibited isometric growth in the lagoon. The mean condition factor obtained was 1.20. The condition factor generally decreased with increase in individual sizes. The major food items were detritus and plant parts. The population of males was significantly higher than the females. The gonadosomatic index showed that M. rume in the Lekki Lagoon uses an average of 7.89% of its body weight in egg production. Fecundity ranged from 741 to 6000 eggs with an average of 2991 eggs per female.
Keywords: length-weight relationship, condition factor, fecundity, mormyrus rume, lekki lagoon, nigeria