Electric Organ Discharge and Electrosensory Reafference in Skates

Skates possess bilateral electric organs that produce intermittent, weak discharges of relatively long duration compared to the discharges of other weakly electric fish. They, like all elasmobranchs, also have an electrosensory system capable of detecting weak, low-frequency electric fields. Several studies have suggested that the discharge is used in some type of social communication. This study measured the strength and nature of the response of the skate electrosensory system to electric organ discharge. Electric organ discharge (EOD) was elicited via electrical stimulation of the medullary command nucleus in two species of skates. The temporal structure and power spectra of the EODs demonstrated that they should be effective stimuli for the skate electrosensory system. The responses of electrosensory afferent fibers in the anterior lateral line nerve (ALLN) to EODs were variable depending upon the location and orientation of the receptor. The responses of most ALLN fibers were very weak compared to the strong reafference produced by the skate's ventilatory activity. Unlike the common-mode ventilatory reafference, EOD reafference was variable in terms of excitation or inhibition, depending upon receptor orientation. Despite the low signal-to-noise ratio observed in ALLN responses to EODs, it is likely that EODs serve as a communicative signal over moderate distances.