The electric organ discharge (EOD) signalling of isolated and of socially interacting Pollimyrus isidori was analyzed.
1. EOD interval histograms of resting animals showed wide ranges with three modes of 12 to 15 ms, of around 92 ms, and of 220 to 230 ms (Fig. 4a). In number and/or position of modes, the P. isidori histograms were clearly different from those shown by four other mormyrid species: Gnathonemus petersii, Mormyrus rume, Brienomyrus niger, Brienomyrus brachyistius.
2. The EOD interval histograms of swimming P. isidori (Fig. 4a) displayed only one mode of around 50 ms and closely resembled the EOD activity exhibited by G. petersii, B. niger, and B. brachyistius.
3. During overt attack (Figs. 4b, 6, 7a), P. isidori displayed high discharge rates as do G. petersii, B. niger, and M. rume. The EOD time patterns of the displays were clearly distinct from the other species' displays.
4. These data suggest the possibility that mormyrids might recognize conspecifics from their resting- or attack-associated EOD time patterns, not, however, by monitoring EOD swimming activity. During this behavior, species identification would seem possible only by the analysis of spectral cues from the properties of the individual EOD pulses (cf. Fig. 3). Compared with the other species mentioned above, the extremely short EOD of P. isidori contains much more energy in a high frequency band (peak: 10 kHz with energy beyond 30 kHz).
5. Different individuals of P. isidori displayed either a Preferred Latency Response of approx. 12 to 14 ms or a response consisting in avoiding a 10 to 20 ms discharge latency to foreign electrical stimuli (Figs. 8–10). While the avoidance response may be considered a jamming avoidance behaviour, reducing the probability of coincidences with a conspecific's EODs, the Prefered Latency Response in P. isidori would have the opposite effect and lsquojamrsquo a conspecific's signals when the latter displays high discharge rates occurring during attack behaviour. Whether these alternative types of latency behaviour are sex, age, or rank correlated remains to be investigated.