Abstract
Fish acoustic communication relies on their hearing capacity. The gas-filled swimbladder has strong acoustic impedance discontinuity with the water and fish tissues and in some fish it has been shown to enhance hearing by transducing the mechanical wave into vibrations that are then communicated to the otoliths. In other species, however, the swimbladder does not appear to contribute to hearing and they are mostly sensitive to particle motion. To investigate the possible role of the swimbladder in enhancing hearing sensitivity in the model species Halobatrachus didactylus , we obtained audiograms using auditory evoked potentials before and after deflating the swimbladder in both males and females. We used three different criteria to estimate the hearing thresholds and compared them to evaluate the impact of the estimation methodology. The different criteria produced audiograms with no statistical difference but there was a statistically significant interaction between the auditory threshold estimation criterium and the sound frequency tested. Importantly, there were no statistical differences between pre- and post-deflation audiograms. These findings suggest that the swimbladder does not play a relevant role in hearing in this species. The Lusitanian toadfish is likely primarily sensitive to particle motion detected by both the inner ear endorgans and the lateral line. The present results are discussed in light of their known ability for resolving fine features of their complex vocalizations.