  Electric fishes modulate their electric organ discharges with a remarkable
variability. Some patterns can be easily identified, such as pulse rate
changes, offs and chirps, which are often associated with important behavioral
contexts, including aggression, hiding and mating. However, these behaviors are
only observed when at least two fish are freely interacting. Although their
electrical pulses can be easily recorded by non-invasive techniques,
discriminating the emitter of each pulse is challenging when physically similar
fish are allowed to freely move and interact. Here we optimized a custom-made
software recently designed to identify the emitter of pulses by using automated
chirp detection, adaptive threshold for pulse detection and slightly changing
how the recorded signals are integrated. With these optimizations, we performed
a quantitative analysis of the statistical changes throughout the dominance
contest with respect to Inter Pulse Intervals, Chirps and Offs dyads of freely
moving Gymnotus carapo. In all dyads, chirps were signatures of subsequent
submission, even when they occurred early in the contest. Although offs were
observed in both dominant and submissive fish, they were substantially more
frequent in submissive individuals, in agreement with the idea from previous
studies that offs are electric cues of submission. In general, after the
dominance is established the submissive fish significantly changes its average
pulse rate, while the pulse rate of the dominant remained unchanged.
Additionally, no chirps or offs were observed when two fish were manually kept
in direct physical contact, suggesting that these electric behaviors are not
automatic responses to physical contact.
