Investigation on Food Ecology of three Cichlid Species in the Mankessim Reservoir, Central Region of Ghana

摘要

The Mankessim Reservoir supports a thriving cichlid fishery that provides both financial gain and nutritional value to the people. Fish samples of Hemichromis fasciatus, Tilapia zillii and Sarotherodon melanotheron were obtained from artisanal fishermen by gill nets (10 m long and 1.5 m deep, 3, 6 and 12 mm mesh) and cast nets (25 mm mesh and 2.5 m radius) in the reservoir (5018''52.08'''N 1001''45.08'''W) from September 2011 to August 2012. Physicochemical parameters were measured in situ and nutrients level determined by the spectrophotometric method. Stomach contents were analyzed using the frequency of occurrence and “points” method and condition was evaluated by means of Fulton condition index. As a result, food resources exploited by T. zillii and S. melanotheron were highly similar. T. zillii fed more on plant material and benthic invertebrates with diatoms (Navicula spp., Pinnularia nobilis, Frustulia rohomboides, Stephanodiscus cymbella, Melosira spp., Gyrosigma spp., Tabellaria sp. and Diatoma sp.) blue green (mainly Ulothrix sp. Oscillatoria spp., Anabaena spp., and Microspora sp.) and desmids being the most preferred algae. S. melanotheron ingested more of debris, and fed on considerable amount of algae and benthic invertebrates mainly chironomid larvae and oligochaetes showing a high level of trophic flexibility. The three cichlids showed very good condition (1.75 ± 0.11 - 1.98 ± 0.40). This could probably be as a result of the observed favourable environmental conditions as all physicochemical parameters were within acceptable limits for their sustenance except for phosphates (1.68 ± 0.04 mg/L to 5.37 ± 0.02 mg/L).