Species Composition and Abundance of the Cichlid Fishes in Owalla Reservoir, Osun State, Nigeria

Abstract

Fish production plays crucial roles in enhancing food security and alleviating poverty of many people in Nigeria. As demand for fish  increases steadily over the years, production becomes inadequate. One of the ways in which adequate fish production could be met is  adequate conservation efforts. This study was conducted with a view of providing a more recent catalogue and update of species  composition and abundance of cichlid fishes in Owalla reservoir. Sampling for cichlids fishes in the reservoir was done monthly for 24  weeks with the use of dugout canoe. Four experimental gillnets, each measuring 2 by 30 m, with various stretched mesh sizes (25.4, 38.1,  50.8 and 63.5 mm) were designed to sample various sizes of the fishes. Other sampling techniques adopted include the use of cast net,  fish traps and hook and line. The six species of cichlid fishes identified during study are Hemichromis fasciatus (SL=7.35±0.12 cm; mean  weight=15.58±9.01g), Sarotherodon galilaeus (SL=11.77±3.12 cm; mean weight=89.48±14.17 g), Oreochromis niloticus (SL=8.35±1.90 cm;  mean weight=36.11±10.02 g ), Tilapia zilli (SL=9.95±1.09 cm; mean weight=88.03±16.04 g ), Tilapia mariae (SL=9.83±1.07 cm; mean  weight=57.81±14.01 g ) and Tilapia dageti (SL=11.12.±2.01 cm; mean weight=85.30±20.01 g). The fish species were adequately  represented, well distributed and occurred frequently in both wet and dry seasons, though the occurrence was higher in the wet season.  The mean values of length and weight recorded for the fishes were small when compared with the values of cichlids from similar  Nigerian inland waters and was attributed to the indiscriminate use of gillnets with unregulated mesh sizes. Overfishing by the artisanal  fishermen could not be ruled out due to lack of regulations on the reservoir. Therefore, regular qualitative and quantitative information  on cichlid fishes in the reservoir is necessary for enhancement of management and appraisal of the fisheries potential of the reservoir  becomes essential.