SUMMARY

The inner ear in most species of fish responds directly to acoustic particle motion rather than pressure. Nevertheless, audiograms are reported with pressure thresholds. It is posited that variations in acoustic particle motion during measurement of hearing thresholds may contribute to inconsistencies observed in sound pressure auditory thresholds reported for damselfish. Hearing thresholds for damselfish in recent literature have been measured with the fish located in water-filled cylindrical waveguides of different materials and sizes resulting in different properties in the acoustic field. Thus, the relationship between acoustic pressure and particle velocity is not the same among all of the reported threshold data sets. These thresholds were also obtained with the fish held at a fixed position in the waveguide. As a result, a change in frequency changes the relationship between acoustic pressure and particle velocity which creates a varying acoustic stimulus over the auditory bandwidth of the fish. In this study, the acoustic fields inside three different waveguides described in the literature were analyzed and compared with the field inside a laboratory waveguide designed for auditory testing. Significant variations in acoustic particle velocity were found as a function of frequency and physical properties of the waveguides. While sound pressure level hearing thresholds obtained in the three waveguides did not match, it was determined that basing the thresholds on acoustic energy density as the metric accounted for much of the variation observed among four different sets of data.