Zebrafish can hear sound pressure and particle motion in a synthesized sound field

Abstract

In order to investigate the hearing capacities of adult zebrafish (Danio rerio), wild type zebrafish were conditioned to both sound pressure and particle motion in a respondent conditioning paradigm. Sound fields were generated by five underwater loudspeakers in a cylindrical tank, which allows separate control of sound pressure and particle motion. Sound stimuli were soft-switched sound pulses having a strength (RMS) of 0.4 to 5 Pa sound pressure (112 to 134 dB re 1 μPa), 6.7 × 10−7 to 6.7 × 10−6 m/s particle velocity or a combination thereof. Frequencies used were 800 Hz or 250 Hz. During the test a fish was placed in the acoustic centre of the tank, confined in a soft nylon mesh fitted with two silver chloride recording electrodes to measure both changes in position and the ventilatory response. Each sound presentation was followed by a brief mechanical jerk of the fish cage (unconditioned stimulus). The startling response to the unconditioned stimulus was thus coupled to the sound signal (conditioned stimulus). Responses were scored as changes in fish position and/or ventilatory rhythm, occurring during or after the sound pulses, but before the unconditioned stimulus. In this way, we found that wildtype zebrafish respond to artificial sounds having either predominantly sound pressure or particle motion. Discrimination of directionally different sounds could not be established. The method is suited well to probe other auditory capabilities, and to test zebrafish mutants lacking one or more otoliths.