Some Aspects of the Biology of Sarotherodon melanotheron and Tilapia guineensis inhabiting Mahin Lagoon, Nigeria

Studies on fish biology are important because they help determine the best management strategy to use in order to conserve fish species in their natural habitat. Thus, some aspects of the Biology of Sarotherodon melanotheron and Tilapia guineensis in the Mahin Lagoon were covered in this study. For the study, 121 fish samples were collected. The sex ratio of S. melanotheron (1:1.64) and T. guineensis (1:1.36) showed no significant deviation from the expected 1:1. Fecundity ranged from 243 to 1223 in S. melanotheron and 156 to 600 in T. guineensis with means of 344.39±166.85 and 286.27±114.85 respectively indicating low fecundity in both species. Observed Gonado-Somatic Index (6.40±3.25% for T. guineensis and 5.65±3.31% for S. melanotheron) suggested the peak of gonad maturity. The regression equation of the length-weight relationship indicated that S. melanotheron exhibited negative allometric growth in male (b=1.66, R2=0.63), female (b=2.80, R2=0.83) and combined sex (b=2.55, R2=0.78) while T. guineensis exhibited positive allometry in male (b=3.05, R2=0.97), female (b=3.04, R2=0.95) and combined sex (b=3.04, R2=0.96). The condition factor was greater than 2 for both species. This study also revealed that the fecundity of the two species was size dependent. Examination of stomach fullness revealed that 4.2% and 0.0% of S. melanotheron and T. guineensis had empty stomachs while 20.0% and 3.8% had full stomachs respectively. This study therefore established that the study area was conducive for the fish. Monitoring and regulation of the fisheries is therefore recommended for conservation and management of the study area.