Electric discharge patterns in group-living weakly electric fish, Mormyrus rume (Mormyridae, Teleostei)

Electrocommunication in weakly electric fish has various functions, such as species recognition and information transfer during social encounters. For communication, weakly electric fish rely on their electric organ discharges (EOD), which are generated by an electric organ located in the fish's tail. While in mormyrids the species-specific EOD-waveform remains rather constant, the highly variable inter-discharge intervals (IDIs) enable the fish to modify their signalling behaviour on a short time scale. Different IDI-patterns were found to correlate with certain behavioural situations. We investigated electrocommunication in a social group of five freely swimming Mormyrus rume during different group behaviours. We found several electrical discharge patterns, which occurred during group foraging, aggressive encounters, fleeing and resting. We were able to describe several so far unknown signal patterns, such as synchronous discharging of two fish, and fixed-order-signalling in groups of up to five fish. Our results show that electrocommunication in social groups consists of complex and rapidly changing interactions between different individuals.