The electric organ discharges (EODs) of Marcnsenius senegalensis, a West African freshwater fish, are bipolar
pulses of short duration (220 ± SE 13µs )I.n males (n= 10; 10.1-13.1 cm standard length-which is around the
size of getting mature), the duration of EOD pulses was of significantly greater variance than in females (n = 9;
9.8-12.8 cm standard length). Male EODs also showed a tendency for a longer duration than female EODs.
Groups of three as well as of 14 M. senegalensis formed temporary schools in a 'naturally' equipped 720-l
tank. While swimming slowly in a loose school during their nocturnal active phase, fish discharged in irregular
long-short-long inter-EOD interval patterns. Near neighbours displayed a tendency to discharge in intervals of
similar duration (nearest neighbour distance < 1/2 fish length).
On removal of a plastic partition that had separated a pair of fish for at least 3 days, mutual threat displays
followed by fighting were observed. During threatening, the fish alternated regularly between bursts of a high
discharge rate and short discharge breaks; the rate of change was 4/s.
The subdominant animal in a group of two was attacked frequently and often ceased discharging when the
dominant fish approached. Courtship behaviour involving gonadally mature fish was accompanied by highdischarge-
rate displays with intervals of constant duration in both fish, and the reciprocal display of 'preferred'
EOD latencies in the 12 ms range.
The results demonstrate electric communication by distinct inter-discharge interval patterns in the social
behaviour of this mormyrid fish.