Swim bladder resonance enhances hearing in crucian carp (Carassius auratus)

Sound sensing is vital for fish and more effort is necessary to address the hearing mechanism in fish. Here, we performed auditory evoked potentials (AEP) measurement, micro-computed tomography (Micro-CT) scanning, and numerical simulation to investigate the resonance of swim bladder and its influence on auditory sensitivity in crucian carp ( Carassius auratus ). The AEP results showed that at the tested frequency range up to 1000 Hz, the mean auditory thresholds of control fishes with an intact swim bladder were lower than that of treated fishes with a deflated swim bladder by 0.38–30.52 dB re 1 μPa. At the high frequency end, control fishes had a high but measurable auditory threshold. Correspondingly, numerical simulations showed that the intact swim bladder had a mean resonance frequency of 826±13.6 Hz, ranging from 810 to 840 Hz while the deflated swim bladder had no predominant resonance peak below 1000 Hz. The amplitude of received sound pressure at the resonance frequency for a sample in control group was 34.3 dB re 1 μPa higher than that for a treated sample, and the acceleration at the asteriscus of the control fish was higher than the treat fish by 43.13 dB re 1 m s-2. Both AEP experiment and modeling results showed that hearing sensitivity is enhanced through resonance of swim bladder in crucian carp and provided additional understandings on hearing mechanism in fish. Summary statement We used AEP measurement, Micro-CT scanning, and numerical simulation to demonstrate that the resonance of swim bladder can enhance hearing in crucian carp. ### Competing Interest Statement The authors have declared no competing interest. * AEP : Auditory evoked potentials SPLp-p : Threshold of sound pressure SALp-p : Threshold of acceleration Micro-CT : Micro-computed tomography 3D : Three-dimensional