The effect of biological and anthropogenic sound playbacks and self-generated movement on the hearing sensitivity of the Oyster Toadfish, Opsanus tau

Abstract

Within the fish inner ear, three otolithic end organs (utricle, saccule and lagena) serve both auditory and vestibular roles. The Oyster toadfish (Opsanus tau) is a vocal fish species that has been extensively studied to understand both the vestibular and auditory functions of the fish inner ear. Previous studies, however, have primarily been conducted on restrained or stationary fishes so it remains unclear how self-generated movement impacts the otolithic end organs. Additionally, the effects of self-generated and anthropogenic sound on fish hearing remains to be known. To address these questions, microwire electrodes were inserted into utricle of free-swimming toadfish using an implantable micromanipulator. Experiments measured the neural response of the utricle to playbacks of conspecific vocalizations at variable speeds while swimming. During movement, fish remained sensitive to conspecific playbacks, indicating that the inner ear can detect auditory stimuli during movement. Additionally, acoustic evoked potential recordings were conducted to measure the auditory sensitivity of toadfish pre- and post-exposure to conspecific vocalizations and anthropogenic sound. Toadfish exhibited auditory sensitivity between 100 and 500 Hz, which overlaps the frequency range of conspecific vocalizations and anthropogenic sound, such as those generated by ship traffic. Exposure to conspecific vocalizations had no significant effect on toadfish auditory sensitivity; however, exposure to anthropogenic sound caused significant auditory impairment that was sustained for at least 3 days. For vocal fishes, the ability to detect and localize conspecific vocalizations is critical for their reproductive success. In the following chapters, I show that toadfish are capable of sound detection while swimming and after exposure to conspecific vocalizations, but their hearing is impaired by anthropogenic sound.