The sense of hearing mediated by the saccule in goldfish

Abstract

The saccule mediates the sense of hearing for many fish species, goldfish (Carassius auratus) in particular. Motions of the swim bladder in response to pressure fluctuations impinge on the saccule of each ear, where auditory-nerve fibers project to medullar, midbrain, and forebrain nuclei in a circuit analogous to the ascending auditory system of tetrapods. It has been repeatedly shown over the past 40 years that the sense of hearing mediated by the saccule has many fundamental features in common with the sense of hearing of tetrapods. Detection and discrimination thresholds for goldfish are in the vertebrate range quantitatively, and are of the same sorts of simple and complex discriminations that mammals and other tetrapods can perform. Furthermore, goldfish behave as if the perceptual dimensions of spectral pitch, complex musical pitch, timbre, and roughness exist for them. Although goldfish do not vocalize, many fish species that hear using saccular input do vocalize (e.g., mormyrids), and have special adaptations for responding to vocalizations, like many tetrapods. Finally, goldfish have been shown capable of simultaneous stream segregation based on the same principles known for humans and other species. Thus, otolith organs can participate in a sense of hearing that is typical for vertebrates.