AFRICAN CLARIAS CATFISH ELICITS LONG-LASTING WEAK ELECTRIC PULSES

The African catfish Clarias is generally considered to possess electro receptors but not electric organs. It is reported here that at least o ne species of the genus, C. gariepinus, can produce weak monophasic di scharges during aggressive interactions with conspecifics. These irreg ular pulse discharges are substantially longer than the electric organ discharges (EODs) of ail other pulse-generating freshwater electric f ishes. It is also shown that the optimal sensitivity of Clarias' ampul lary receptors just corresponds to the modal pulse duration. The Clari as catfish, with its very specific EOD, may be of special interest in the evolution of the electrogenic system in the siluriforms, comprisin g many electroreceptive but nonelectrongenic catfish species.