Variability of the bioelectric field of the catfish Ictalurus nebulosus (Le Sueur, 1819; Pisces, Teleostei, Siluriformes)

The electric dc-field of Ictalurus nebulosus (Teleostei, Siluriformes) was recorded by having two specimens swim through a silk screen cylinder at 5 cm distance from two recording electrodes, during an observation period of three months. The dc-field was usually rather stable; on average potential differences of 37 and 55 mu V in water with resistivities of 33 and 48 ohm. m respectively were recorded. From time to time the field strength suddenly increased by a factor of 10, after which the field returned to the original value within about 15 min. Increases of field strength could also be evoked by presenting food, ``beef juice'', and by approaching the tank. We propose that the recorded changes in bioelectric field strength reveal a particular, perhaps stress-or arousal-related, physiological condition, and that they are sufficiently strong to be perceived by electrosensitive conspecifics.