Efficiency and selectivity of gillnet mesh sizes for assessing fish composition of egbe water reservoir, Ekiti State, Nigeria

Comparism of five (5) different gillnet mesh sizes ranging from 50.8mm, 63.5mm, 78.2mm, 88.9mm, and 101.6mm was done at four (4) different sampling stations along the banks of the reservoir to evaluate the efficiency and selectivity of gillnet mesh sizes for assessing fish composition in Egbe water reservoir, between April, 2014 and January, 2016. The nets were set at 6.00pm and hauling done in the morning at 8.00am, fishermen were well monitored to avoid sampling bias and ensure a constant fishing effort. The fishes were sorted into separate container based on gillnet mesh sizes and also species. The total length and weight of individual were taken, Simpson’s index, Simpson reciprocal index and Evenness were also determined. The percentage composition by biomass fish landing was recorded. 31,905 fishes belonging to 7 species and 5 families were recorded. The most abundant family was the Cichlids represented by 3 major species, Oreochromis niloticus, (25.41%), Coptodon zillii (17.59%), and Tilapia guineensis (15.74%) while Clarias gariepinus (15.07%) belong to the Clariidae. Also, Parachanna obscura (13.45%), Hepsetus odoe (7.08%) and Heterotis niloticus (5.67%) belong to the family Channidae, Hepsetidae and Osteoglossidae respectively. Simpson’s index of diversity 0.46, Shannon – weiner (H) (1.98), Evenness (E) (1.61) and Margalef”s index (0.94). All the five gill nets captured all the fish species but the smallest gill net mesh size (50.8mm) (43%) captured more of O.niloticus and greater number than others, this shows that the smaller gill mesh nets were more efficient for capturing more fishes than other graded mesh nets, but should be discouraged for artisanal fishing activities in the study area, other gears like hook and line, cast nets and traps should be encouraged.