Re-evaluation Survey of Fish Composition, Abundance and Distribution in Agbokim Waterfalls, Nigeria

Abstract

Alterations in the diversity of the ichthyofauna of a tropical waterfalls system can be affected by unsustainable utilisation of the fisheries resources, anthropogenic activities, runoff from faulty agricultural practices and environmental perturbation. To re-establish the status of the fish composition and diversity of Agbokim Waterfalls, monthly fish samples obtained from the fishery and physico-chemical properties were investigated in rainy and dry seasons, for six months along the length of the three reaches of the waterfalls. The results revealed a total of 833 fish specimens representing 18 species belonging to 15 genera from 9 families which is in deficit of four fish species, in the previous study which are Alestes nurse (Characidae), Aphyosemion gardneri (Cyprinodontidae), Pelmatochromis guntheri and Hemichromis fasciatus (Cichlidae). Cichlidae, Clariidae and Bagridae were the most abundant families accounting for 54.4% of the total catch with Cichlidae (23.17%) as the most dominant family and Mockokidae (1.68%) as the least with Tilapia zillii (15.4%), Clarias gariepinus (10.9% ) and Chrysichthys nigrodigitatus (9.5%) as the most dominant species accounting for 35.8% and Synodontis clarias (1.7%) with the least abundance. Fish species distribution in the downstream reach was dominant with 15 taxa and 607 (72.9%) individuals and in the midstream reach with 11 taxa but least (12.6%) number of individuals. Shannon Wiener diversity index for the six months was 2.7101 with Evenness value of 0.9376. The Richness index of Margalef’s was 2.5279 and Menhinick’s 0.6237. Seasonal variations in physico-chemical properties showed that, dissolved oxygen and conductivity were significantly (P< 0.05) higher in the raining season while pH showed no significant difference (P > 0.05). Temperature was significantly higher (p < 0.05) in the dry season than in the raining season. The hydrological properties showed a significantly higher mean values of rainfall (364.67± 0.00 mm) in the rainy and transparency (45.55± 1.58) in the dry season at (P < 0.05). In order to determine the cause of decline in fish species composition and abundance, further research on the heavy metals profile of the waterfalls is suggested.