Electric Discharges as Species-Typical Signatures

The electric organ discharges of the mormyrid electric fish may be described as having two parts:  a relatively fixed Electric Organ Discharge (EOD) waveform, and a variable sequence of pulse intervals (SPI).  The fixed EOD waveform is controlled by the anatomy and physiology of the electric organ;  the variable sequence of intervals is controlled by the pacemaker in the brain.
EODs versus SPIs
The oscilloscope tracing (left) shows the fixed waveform of the EOD on an expanded time scale.  The sequence of pulse intervals is plotted on a more condensed time scale (right).  The species illustrated here is an undescribed species of Brienomyrus from Gabon   (From Hopkins, 1986)

To hear the EOD or the SPI, click on the pictures above.


Individual Differences in EODs.  A given individual produces a highly stereotyped EOD waveform with little variation.  The ten EODs shown in (a) were all recorded at different times from the same individual.  The 12 EODs shown in (b) were recorded from a second individual.  In each case,  the EODs were normalized to the same amplitude.  Different individuals of the same species produce similar, but often not identical EODs.  In (c),  there are nine different individual's EODs superimposed.   All of these are females and juveniles.  In (d)  there are three different males superimposed.

From:  Hopkins (1983)

Sex Differences in EODs.  The most pronouncced variation in this example relates to the sex of the fish.  The EODs of males are much longer in duration than those of  females.

Species Differences in EODs.  The EODs of different species that live in the same environment often diverge,  creating a community of EODs with enormous diversity.  As an example,  click here to see the EODs of other Mormyrids of Gabon.

References

Hopkins, C. D. (1981). “On the diversity of electric signals in a community of mormyrid electric fish in West Africa.” American Zoologist 21: 211-222.

Hopkins, C. D., Ed. (1983). Neuroethology of species recognition in electroreception. Advances in Vertebrate Neuroethology. New York, Plenum.

Hopkins, C. D. (1983). Sensory mechanisms in animal communication. Animal Behaviour 2: Animal Communication. T. R. Halliday and P. J. B. Slater. Oxford, Blackwell Scientific Publications. 2: 114-155.

Hopkins, C. D. (1986). Behavior of Mormyridae. Electroreception. T. H. Bullock and W. F. Heiligenberg. New York, John Wiley & Sons: 527-576.

Hopkins, C. D. and A. H. Bass (1981). “Temporal coding of species recognition signals in an electric fish.” Science 212: 85-87.

Moller, P. (1995). Electric Fishes: History and Behavior. London, Chapman & Hall.