The effect of a man-made lake on the diet of the African electric fish Mormyrus rume Valenciennes, 1846 (Osteoglossiformes:: Mormyridae)

The diet of 223 specimens of Mormyrus rume (Mormyridae) from the Bia River on which a hydro-electric dam was built in 1959, was studied in relation to locality, season and fish size. A feeding index was computed by combining the occurrence, numerical and weight percentages of the items identified in the stomach contents. This index showed that M. rume in the river ate prin cipally invertebrates, especially chironomid larvae. In contrast, M.. rume from the man-made lake contained mostly phytoplankton. This difference was statistically significant. In the lake, chironomid larvae and Bacillariophy ceae constituted the main source of the diet of young fish. In larger speci mens, Chaoborus sp. formed the main part of the diet. No significant tempor al variation occurred in the dietary composition. The overall food composit ion was similar in each locality of the Bia River from one period to anothe r.