2017, Vol. 2 Issue 2, Part DECEMBER
Community dynamics of the fishes and some aspects of the limnology of two West African reservoirs
Author(s): Ali F. A., Ofori-Danson P. K., Nunoo F. K. E., Idowu, R. T. and Tayib Y.
Abstract: The ichthyofaunal diversity and limnology of Kpong and Oyun reservoirs located in Ghana and Nigeria respectively were studied with the main aim of gathering useful information to support the development, management and sustainable use of their respective fisheries to enhance the socio-economic status of riparian communities. Experimental fishing with a battery of gill nets of various mesh sizes was used to sample for fishes monthly (September 2014 to August 2016) were individually identified, weighed and measured for standard and total lengths. Water samples were taken monthly and analyzed for physico-chemical parameters. Cichlidae and Mormyridae were the most abundant families in Kpong reservoir accounting for 77.7% and 8.7% respectively and Mochokidae was the least occurring with 2.0% while Oyun recorded Cichlidae, Claridae and Mormyridae as the most important families encountered with 45.99%, 25.41% and 12.2% respectively with Channidae (0.5%) the least occurring. In the Kpong Reservoir, 17 species belonging to 5 families were encountered with Oreochromis niloticus (28.94%) and Sarotherodon galilaeus (25.98) the most abundant and Gnathonemus cypriniodes (0.43%) the least. In the Oyun Reservoir, 18 species, representing 9 families, were obtained. Tilapia zilli (22.78%) and Oreochromis niloticus (14.14%) were the dominant species with Channa obscura (0.50%) the least. The fish diversity of the Kpong Reservoir was lower than that of the Oyun reservoir recording a species diversity (H’) of 2.14 compared to 2.45 for Oyun. Herbivorous fishes were dominant in the two reservoirs while carnivorous ones were the least dominant. The Forage-Carnivore (F/C) ratios of 1.21 (by number) and 2.13 (by weight) for Oyun and 3.49 (by number) and 1.72 (by weight) for Kpong suggest a suitable ecological balance between carnivorous fishes and their prey populations. The estimated potential fish yield per year for the Oyun Reservoir (97.61kg/ha/yr) was higher than that of the Kpong Reservoir (60.69kg/ha/yr) possibly due to its shallower nature and higher productivity. Both reservoirs were well oxygenated all year-round with Oyun exhibiting a weakly acidic pH to Kpong’s weakly basic trend. The key physico-chemical parameters in both reservoirs were within ranges for fish survival and production with Oyun being characterized by a comparatively higher ionic and nutrient content. Nutrients displayed greater impact on fish abundance hence the inference by the study that nutrient levels fluctuations are factors that play crucial roles in fish abundance in both reservoirs. Granted the adoption of appropriate management measures, both reservoirs are considered highly productive and possess the potential to optimize their fish production.