Listening in the dark—Auditory evoked potential measurements and novel imaging techniques elucidate the role of hearing in deep sea fishes

In the aphotic zone of the deep ocean, mechanisms for conveying information to conspecifics or gathering information about the environment and potential predators are subject to the same physical and ecological limitations as near to the sea surface with the addition of no available light. Passive or active communication often utilises bioluminescent visual, olfactory, or acoustic signals. The sensitivity of deep sea fish to sound has never been tested. In a multi-disciplinary study, deep sea fishes were sampled in the Indian Ocean and examined for acoustic sensitivity. Acoustic signals were generated in a tubular steel tank using a calibrated sound source with pressure and particle motion of generated signals measured. The auditory sensitivity was tested using the auditory brainstem responses to amplitude modulated stimuli. To determine if the pressure or particle motion component of the acoustic signals was most relevant, specimens of all species tested were imaged in a micro-CT using a modified contras...