The electric fish Brachyhypopomus pinnicaudatus produces jamming avoidance responses to signals that are harmonically related to its own discharges.

Jamming avoidance responses (JARs) are exhibited by pairs of pulse type electric fish that discharge with similar frequencies whenever their individual pulses are about to coincide: responses consist of the transient shortenings in inter-discharge intervals in the fish with the higher frequency. This study describes and models novel forms of JARs observed in sexually mature male or female Brachyhypopomus pinnicaudatus. One novel JAR was observed in male-female pairs in their natural habitat. It happened when the baseline frequencies were not similar but, rather, when one was almost twice that of the other; moreover, the transient interval shortenings occurred not in the fish with the higher frequency but in the slower one. Transient interval shortenings similar to those in all natural JARs were observed in individual fish in tanks and submitted to periodic electrical pulse trains. They happened not only when pulse frequencies were slightly lower than the unperturbed frequency emitted by the fish but also when slightly lower than the frequency's sub- or higher harmonics (e.g. one half or twice). The proposed model satisfactorily reproduces all experimental observations. In it, forthcoming inter-pulse intervals reflect the differences between the cophases of pulses that arrive within the 'sensitive windows' belonging to either consecutive (i.e. one and the next) or alternating (e.g. every other, every three) intervals. Paired pulse fish embody interacting oscillators, and, in particular, JARs embody either quasiperiodic phase walk-throughs and intermittencies or periodic and locked forms. Hence, their study would profit by the powerful theories and approaches advanced by nonlinear dynamics.