Monopolar electric discharges of the catfish <Emphasis Type="Italic">Parasilurus asotus</Emphasis> (Siluridae,Siluriformes)

Electric discharges in the catfish Parasilurus asotus are registered for the first time. The discharges are monopolar pulses of a 50–300 ms duration which corresponds to the frequency characteristics of ampoules of electroreceptors in these catfish. Electric generation is discovered only upon the aggressive-defensive behavior of not less than two species. In solitary fish no discharges were observed neither at prolonged continuous registration (longer than 24 h each) nor at mechanical stimulation. The hypothesis is discussed of a potential mechanism of active (under use of their own electric discharges) monitoring of water conductivity with a relative sensitivity on the order of 0.0002%. This hypothesis may be applied to an explanation of anomalous group behavior of these catfish before earthquakes.