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Abstract. The African catfish Clarias is generally considered to possess electroreceptors but not electric organs. It is reported here that at least one species of the genus, C. gariepinus, can produce weak monophasic discharges during aggressive interactions with conspecifics. These irregular pulse discharges are substantially longer than the electric organ discharges (EODs) of all other pulse-generating freshwater electric fishes. It is also shown that the optimal sensitivity of Clarias' ampullary receptors just corresponds to the modal pulse duration. The Clarias catfish, with its very specific EOD, may be of special interest in the evolution of the electrogenic system in the siluriforms, comprising many electroreceptive but nonelectrongenic catfish species.

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