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.
Odontocetes have developed a broadband sound reception system that performs well underwater. We used aluminum materials and soft silica gels to fabricate a bio-receptor to mimic the sound reception system of a finless porpoise. Both numerical modeling and experiments suggested that compared to omnidirectional reception, the porpoise-inspired receptor can achieve broadband and directional sound reception with frequencies ranging from 15 to 90 kHz and enhance the reception by an average of 3.9 dB in this bandwidth. At some frequencies, this reception improvement can reach 7.3 dB in experimental data. This work provides an alternate idea to design sound receptors to be applied in underwater broadband and directional sound reception.
Odontocetes have evolved special acoustic structures in the forehead to modulate echolocation and communication signals into directional beams to facilitate feeding and social behaviors. Whistle directivity was addressed for the Indo-Pacific humpback dolphin ( Sousa chinensis) by developing numerical models in the current paper. Directivity was first examined at the fundamental frequency 5 kHz, and simulations were then extended to the harmonics of 10, 15, 20, 25, and 30 kHz. At 5 kHz, the –3 dB beam widths in the vertical and horizontal planes were 149.3° and 119.4°, corresponding to the directivity indexes (DIs) of 4.4 and 5.4 dB, respectively. More importantly, we incorporated directivity of the fundamental frequency and harmonics to produce an overall beam, resulting in −3 dB beam widths of 77.2° and 62.9° and DIs of 8.2 and 9.7 dB in the vertical and horizontal planes, respectively. Harmonics can enhance the directivity of fundamental frequency by 3.8 and 4.3 dB, respectively. These results suggested the transmission system can modulate whistles into directional projection, and harmonics can improve DI.
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