Abstract
The current study demonstrated that juvenile Mormyrus rume proboscirostris , an African freshwater weakly electric fish, used their active electrosense in group cohesion. Data also indicated that sight and mechano‐reception could play a synergistic role in controlling this behaviour. The developmental change from a larval monophasic electric organ discharge to the adult biphasic waveform was accompanied by a reversal of the fish's social spacing. Light was aversive to social spacing in the younger fish (aged 49 and 65 days), but facilitated aggregation in the older fish (245 days).