Diversity, distribution and abundance of fish species in Lake Asejire, Oyo State, Nigeria

Aquatic systems in Nigeria have suffered stress induced by human activities which alter the natural composition of the water resources. This study investigated the diversity, distribution and abundance of fish species in Lake Asejire. The lake was partitioned based on accessibility into upper, middle and lower sections for the study. Fish species were sampled using monofilament gill nets with stretched mesh sizes ranging from 44.45-169.33mm. Water and fish species were sampled fortnightly for a period of twelve months. Water quality parameters: temperature (28.96±0.28oC), dissolved oxygen (5.6±0.13mg/l), pH (6.73±0.19) and conductivity (159.8±0.32μS/cm) measured were within suitable standard ranges for fish production in natural waters. A total of 16 species from 10 families were identified from the lake. Cichlids had the highest number of fish species (4) and relative abundance (66.82%) and Coptodon zillii was the most abundant fish species across the months and sampling stations (27.53%). The lower section of the lake had the highest relative abundance (52.90%) while the upper section of the lake had the least (16.14%) and the highest fish catch (13.35%) was in November. The species richness of the lake decreased from lower (S=16) to upper section (S=14), the middle section was highly diversified (H=0.73) with a combined value of H=0.67 for the lake. The fish species were evenly distributed across the lake with the highest evenness in the upper section (E=0.22). Simpson’s index was highest in the lower region (D=0.30) and there was a high probability of picking different fish species at random. Trophic grouping showed forage to carnivore (F/C) ratio of 2.06 indicating an unbalanced fish population based on food habit, which should be addressed. There is need for proper regulation such as enforcement of fishing seasons and fishing across the trophic levels to ensure sustainability of the fish resources in the lake.