Springer Online Journal Archives 1860-2000
Summary 1. A survey of abundance, distribution, and electric organ discharge (EOD) activity of mormyrid fish as well as associated aquatic conditions was conducted in a selected study area, 8 km upstream in the Swashi River, a tributary of Lake Kainji, Nigeria (Fig. 1). 2. Mormyrid locomotor activity and EOD repetition rate exhibited a daily activity rhythm (Fig. 2) with changes in light intensity and possibly temperature (Fig. 3b) affecting the onset and offset of the fish's nocturnal activity period. 3. Eight sympatric mormyrid species were collected: Petrocephalus bovei, Marcusenius cyprinoides, M. senegalensis, Mormyrops deliciosus, Mormyrus rume, M. hasselquisti, Hyperopisus bebe, and Pollimyrus isidori (Table 1). 4. The distribution of mormyrids with regard to pulse type, time of day, and microhabitats (inlet, opening of inlet, and river) was analysed. During the night, mormyrids were most abundant at the inlet's opening, while during their (daytime) inactive period, most EODs were monitored inside the inlet (Fig. 5: T). At the inlet's opening, a temporal separation of species (related to pulse duration, Fig. 5: S1 and S2) suggested the existence of a temporal resource partitioning mechanism.
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