Paramormyrops tavernei, TAVERNEI (POLL, 1972)

Figure 2. Electric organ discharge (EOD) waveforms recorded from 40 specimens of P. sphekodes-like mormyrids from the Ogooué River Basin of Gabon suggest the possibility of two species with distinct EOD waveforms. (A) For each specimen, EOD duration is plotted against standard length (SL). (B) Histogram of EOD durations reveals two modal peaks: one for short EODs, <2 ms duration, and one for longer EODs,> 2 ms. (C) EOD waveforms of longer (above) and shorter duration (below) are superimposed after each EOD’s amplitude is normalized to the same peak-to-peak height and centred on the zero-crossing between positive and negative peaks. Blue lines are males and red lines are females. Head positivity is upward. EOD duration is measured between T1 and T2 (in E), first and last points of the waveform that deviate above or below the baseline by more than 2% of the peak-to-peak height. In previous publications, the longer EOD type was referred to by the code name ‘SN4’. The fish with the ‘short EOD’ waveform is new to this study. (D) Histograms of SLs of all 40 specimens separated by EOD-type and by sex/age class show that within each EOD type there are males recognized by their dimorphic anal fins.Within each group, males tend to have the longest duration waveforms.This sex difference is especially pronounced for SN4 males recorded during the breeding season. Fish of both EOD types co-occur at two sites in Gabon: the main channel of the Ogooué River at Doumé and the Sébé River nearby (see map). (E) EOD waveform of specimen CUMV 98177 tag JPS-1238 showing how EOD duration is measured.