Abstract:

Many species of deep‐sea fish have special sensory adaptations to help them survive at great depths and with lack of light. While such adaptations are best known in the visual system, it is likely that there are also auditory system adaptations that enable the fish to make use of the auditory scene. However, there are few data on the auditory system of deep‐sea fish. The study compared inner ear structures between several such species. Some features in the ears in the species studied were similar to structures associated with enhanced hearing ability in the ears of some shallow water hearing specialists. These findings support the hypothesis that some deep‐sea fishes have evolved specializations for hearing. We also report some features in the ears of deep‐sea fishes that have never been seen in the ears of other vertebrates. These include specializations in the orientation of sensory hair cells, diversity in hair cell ciliary bundle shapes, and a number of unique otolith characteristics. While it is not possible to test hearing in deep‐sea fishes, the various adaptations found suggest that at least some have evolved highly specialized adaptations to enable them to use sound in the deep sea.