Behavioural analysis of electric signal localization in the electric fish, Gymnotus carapo (Gymnotiformes)

Abstract

This study investigates how an electric fish is able to localize in space the electric signals from another fish. South American electric fish of the pulse-species, Gymnotus carapo, were housed in a large, circular arena with a shelter in the centre and non-moving electrical models which mimicked the discharge of a conspecific were presented at the edge of the tank. Gymnotus, a naturally aggressive fish, approached and threatened these electrical models. The nocturnal fish were observed approaching the electrodes under near-infra-red light, and the paths to five different geometrical arrangements of electrodes were compared. The results suggest that Gymnotus cannot determine the direction or distance of an electrical source placed in its territory but that they can approach the electric stimulus by aligning their body axis parallel to the electric field vector while swimming. By using this simple strategy they are able to find the source in a reliable, although indirect, way. Gymnotus showed a slight polarity preference for approaching the head of the model fish. These fish did not discriminate between a diverging electric field and a converging electric field. They were well-oriented to the vector direction even when the magnitude of the current was relatively homogeneous. Gymnotus appears to maintain its alignment to the electric field vector by an active hunting movement.