Limnological Evaluation of the Fisheries Potentials of a Ghanaian Reservoir
Morpho-edaphic Index (MEI), and total nutrient input have been applied to the Dawhenya reservoir in Ghana from August 2006 to July 2007 to estimate existing fish yield and future potential productivity. The estimated existing fish yield from the reservoir was about 38.44 kg/ha. In the Dawhenya reservoir, 12 species belonging to 8 genera were encountered out of which 7 genera were fin fishes while the remaining genus was a shell fish. During the dry season, eight fish species were sampled and Barbus macrops contributed the highest (71.6 %) and Oreochromis niloticus the lowest (0.2 %) by weight while in the wet season five fish species were collected and Barbus macrops contributed the highest (85.3 %) and Macrobrachium vollenhovenii the lowest (2.1 %) of total weight of fish in drag net catches. Estimates of b-values ranged from 2.793 in Sarotherodon galilaeus to 3.267 in Macrobrachium vollenhovenii. Only Barbus macrops growth pattern in the reservoir was isometric meaning there was an equal increase in length and weight during growth, while Macrobrachium vollenhovenii, Macrobrachium macrobrachion and Sarotherodon galilaeus growth patterns were allometric, meaning increases in length and weight of the species were not equal during growth. The general physicochemical parameters monitored during the study period fell within the ranges suitable for fisheries and aquatic life in reservoirs, except for phosphates which were outside recommended ranges. Observations of pH showed that the reservoir was slightly alkaline. Agricultural activities within the catchment area of the reservoir should be monitored and controlled to prevent nutrient enrichment since the inhabitants were predominantly peasant farmers.