Fish fauna of Agbokum waterfalls in South Eastern Nigeria

Knowledge of ichthyofauna of waterfalls is important in the development and management of conservation measures. In order to establish the fish composition and diversity of a tropical waterfalls monthly fish samples and physic-chemical parameters were investigated in wet and dry seasons, over a two year period in three regions along the length of Agbokum waterfalls. Water turbulence, size of river, flow velocity, water level, temperature, transparency and food availability explained the observed seasonal and spatial changes in fish abundance. Five thousand four hundred and eighty four (5484) fish representing 22 species belonging to 16 genera from 9 families were sampled in both dry and wet seasons, with 10 species being restricted to wet season and only 1 in the dry. Cichlidae, Clariidae and Cyprinidae were the most abundant families accounting for 56.7% of the total catch with Tilapia zillii, Clarias gariepinus and Labeo coubie dominating overall catch constituting 35.5%. Among the three dominant species, two benthic fishes (L. coubie and C. gariepinus) showed inverse distributional pattern with Clariid fish (C. gariepinus) most abundant downstream and least represented upstream. Cyprinid (L. coubie), on the other hand, dominated the upstream reaches and scarce downstream. Five species were site specific because of the association with only the midstream portion of the river (L. senegalensis), upstream (A. gardneri, A. filmentosus and E. sexfasciatus) and downstream reaches (H. fasciatus, A. occidentalis and C. nigrodigitatus). The two benthic species (C. gariepinus and L. coubie) produced a bimodal size class distribution in the three sites while T. zilli showed tri-modal size class. Equitability index (E) was generally low ranging from 0.03 (midstream) to 0.14 (downstream). Downstream reaches recorded highest diversity throughout the year with higher values for the wet season samples than dry. Wet season and Downriver region of the waterfalls were therefore critical in maintaining fish stock of the water falls.