For a complete library of Gymnotus EODs visit a web version of Electric Fish Waveform Analyzer. Double click on species under “choose a file to graph”
Gymnotus generate a continuous pulsed electric organ discharge (EOD). The repetition rate of this discharge is usually within a species typical range although there is much overlap in discharge rates between species. Most species generate EODs with a repetition rate of somewhere between 20 and 80 Hz. During the day EOD rates are lower and more stable than during the night when Gymnotus are active. Gymnotus modulate the EOD rate considerably during social interactions – with sudden or slow rises and falls in EOD rate and switch-offs of the electric organ lasting from seconds to several minutes.
There is considerable diversity of EOD waveform in Gymnotus expressed by the number of phases of alternating polarity (1-5) and the relative duration and amplitude of each of these phases (see figure below). Gymnotus species living in syntopic local assemblages have species characteristic EOD waveforms with no partitioning of signal space.
Phylogeny of Gymnotidae with photographs, EOD waveforms and power spectra for at least one species of each genus, and representing all major EOD waveform shape variation within each genus and within each of three principle Gymnotus clades, A-C (1-9). Tree topology from Albert et al. (2004b). EODs normalized to peak-to-peak amplitude and aligned to the largest positive peak. Scale bar = 1 ms. Fourier power spectrum normalized so that peak energy is adjusted to 0 dB. Vertical axis = amplitude (0 to –42 dB). Horizontal axis = frequency (0 to 10 kHz) with Peak Power Frequency reported in inset text.
Crampton, W.G.R ., and Albert, J.S. (2005) Evolution of Electric Signal Diversity in Gymnotiform fishes. In. Fish communication (Ed. B.G Kapoor, F. Ladich, S.P. Collin, P. Moller). Scientific Publisher Inc. Enfield, in press.