“Electromotor” Response in the Electric Fish Eigenmannia (Rhamphichthyidae, Gymnotoidei)

Abstract

VARIOUS species of fish are known to emit and perceive weak electrical signals^1–4. Whereas the physiological mechanisms involved in the production and perception of such signals have been investigated in detail (ref. 3, pages 347 and 493), less is known about their behavioural relevance. Lissman² proposed and gave evidence for a role in object detection, by the distortion of the fish's own electrical field due to either dielectric or conducting objects within range. This idea has been supported by later work (refs 4–6 and personal communication from A. Kalmijn and R. Adelman). The study reported here was undertaken as a first effort to devise ways of measuring the performance of the object detecting system in respect to its discrimination of particular parameters such as distance, size and motion. A primary goal was to find methods based on built-in responses, rather than time-consuming conditioning procedures, which could be used on any individual on a given day to assess its skill in relation to species norms and would thus facilitate the quantification of changes in performance after nerve transections, brain lesions and such like.