Further analysis of the individual discharge characteristics predicting social dominance in the electric fish, Gymnotus carapo

Abstract

The electric organ discharge (EOD) behaviour of Gymnotus carapo was analysed in isolated fish with no previous experimental experience. All animals were then allowed social interaction (4 hr total), and were finally retested in isolation. Each of the two individual testing sessions consisted of four trials per fish, during which frequency histograms of the EOD intervals were accumulated. The results showed that the histograms were invariably multi-modal, and the reasons for this were examined. They were then subjected to a computer-aided statistical analysis, and various features were shown to be related to the dominance status of the fish determined in the second part of the study. A subsequent experiment performed 6 months later demonstrated sequential frequency ‘shifts’ in resting isolated Gymnotus. These shifts are discussed in terms of the interval histogram results, and it is suggested that they represent a type of social advertisement. Finally, a hypothetical physiological mechanism is proposed to account for the observed EOD distributions.