DIURNAL MOVEMENTS AND DISCHARGE CHARACTERISTICS OF ELECTRIC GYMNOTID FISHES IN THE RIO NEGRO, BRAZIL

¹ Department of Physiology, University of California, Berkeley, California 94720

Gymnotids of 13 species were trawled in water 10-20 m deep; all emitted weak electrical discharges. Each fish had a typical frequency of discharge; each species had a typical range of frequency but there were overlaps between species. Waveforms of discharge were similar in several species. Electric organs were derived from muscle tissue in most low frequency species and from nerve tissue in high frequency species. Diurnal movements of fishes were followed electronically. Fishes formed aggregations in 15-20 m deep water about 100 meters from shore during the day and dispersed along the shore at night. Individual daytime aggregations were re-established each morning.

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