Abstract
The primary hearing organ in most fishes is the saccule, which contains a calcareous otolith composed of aragonite and its associated sensory epithelium. In some fish populations, particularly salmonids, the aragonite in the saccular otolith is partially or mostly replaced by vaterite, a phenomenon known as otolith crystallization. Despite the relatively common occurrence of otolith crystallization, the cause of this switch in calcium carbonate type and the consequences for the fish are not understood. The present study looks at both proximal and distal mechanisms that may contribute to otolith crystallization in various salmonid species, particularly with regard to environmental stress and physiological consequences of that stress. Structural and functional data on the ears of salmonids with crystallized otoliths will also be presented. Auditory evoked potential recordings from juvenile chinook salmon demonstrated that fish with at least one vaterite otolith have significantly increased hearing thresholds compared to conspecifics with two aragonite otoliths. These findings suggest that otolith crystallization can have potential negative consequences for the animal.