Patterns of electric organ discharge activity in the weakly electric fish Brienomyrus niger L. (Mormyridae)

Abstract

In this study we investigated the electric organ discharge (EOD) activity of the mormyrid fish Brienomyrus niger when they were not affected by conspecific EODs. The fish emitted two types of EOD patterns: phasic and tonic sequences of pulse intervals (SPIs). The phasic SPI occurred in the form of stereotyped, individual-specific bursts in EOD activity which we called scallop. Tonic SPIs varied in mean EOD repetition rate and pulse interval stability, and consisted of either regular activity with mean frequencies exceeding 10 Hz and a coefficient of variation (cv) below 15%, or variable activity with mean rates below 10 Hz and cv's of 15% and above. Individual fish predominantly generated one of the three patterns: "variable", "regular", or "scallop". Most fish emitted "variable" activity, but "regular" activity was typical of females and "scallop" of males. We suggest that these SPIs may facilitate individual recognition. The dynamics of the electromotor command system, as reflected by the fish's EOD activity, is compared with that of the well-studied mammalian inferior olive, and mechanisms for a possible self-regulatory central pattern generator are discussed.