Electric communication in fish and the problem of recognizing very brief waveforms

Abstract

Pulse-type, weakly electric fish produce brief, low voltage, electric discharges continuously at between 10 and 100 Hz throughout their lives. The pulses are generated by specialized electric organs which set up dipole electric fields in the surrounding water. Objects or surfaces in the vicinity distort the field and provide the fish with a navigational system ideally suited to their nocturnal niche. The field geometry is monitored by a dense array of electroreceptors, the neural transducers of this unique electrosensory system. Their extreme sensitivity has been exploited for a second function, that of electric communication. The speciesspecific mean discharge rate, its temporal patterning, and the pulse waveform are used to code a rich variety of social signals including the species, sex, age, aggression and readiness to mate of the sender as well as complex agonistic and courtship messages. One of the long-standing problems in electric fish research has been to understand how these animals analyse such brief waveforms. In this article I describe a new hypothesis which involves the recognition of the characteristic beat patterns established when sender and receiver fish discharge in near synchrony. We have recently been testing this idea both in the laboratory and in the field in South America.