Population structure and phenotypic variability of cichlids in Asejire Lake, Nigeria

Abstract

Population structure and phenotypic variability of cichlids of the hydrodynamic, Asejire Lake was investigated. Four cichlid populations, Oreochromis niloticus, Sarotherodon galileaus,Tilapia  zillii and Hemichromis fasciatus were identified. These species constituted 36.65% of the total observed fish catch of the Lake. T. zillii dominated the cichlids, while H. fasciatus was the least (19.92% and 2.67% of total catch respectively), having 15.30 and 12.70 cm maximum total length respectively. Coefficient of phenotypic variability (CV) was not significantly different (p > 0.05) between the predominant and the least dominant species. In T. zillii, homogeneity (CV<10%) occurred in 55% phenotypic traits while body depth, and fin lengths (dorsal, caudal, pectoral and pelvic) were heterogeneous (CV>10%). Whereas, in H. fasciatus, homogeneity occurred in five phenotypic traits while six were heterogeneous (body depth, and fin lengths (anal, dorsal, caudal, pectoral and pelvic). There was significant correlation (p.corr=0.0024) in variability of phenotypes of T. zillii and H. fasciatus. In conclusion, both the predominant and the scarce tilapia species were adapting to prevailing environmental condition of the lake through flexibility of body depth and fin morphology. This trend of adaptation could emanate from attempt to overcome hydrodynamic situation, conditioned by frequency of dams’ gate valve opening.