Abstract
Despite the diversity in fish auditory structures, it remains elusive how otolith morphology and swim bladder-inner ear (= otophysic) connections affect otolith motion and inner ear stimulation. A recent study visualized sound-induced otolith motion; but tank acoustics revealed a complex mixture of sound pressure and particle motion. To separate sound pressure and sound-induced particle motion, we constructed a transparent standing wave tube-like tank equipped with an inertial shaker at each end while using X-ray phase contrast imaging. Driving the shakers in phase resulted in maximised sound pressure at the tank centre, whereas particle motion was maximised when shakers were driven out of phase (180°). We studied the effects of two types of otophysic connections-i.e. the Weberian apparatus (Carassius auratus) and anterior swim bladder extensions contacting the inner ears (Etroplus canarensis)-on otolith motion when fish were subjected to a 200 Hz stimulus. Saccular otolith motion was more pronounced when the swim bladder walls oscillated under the maximised sound pressure condition. The otolith motion patterns mainly matched the orientation patterns of ciliary bundles on the sensory epithelia. Our setup enabled the characterization of the interplay between the auditory structures and provided first experimental evidence of how different types of otophysic connections affect otolith motion.
Highlights
Otoliths of modern bony fishes (Teleostei) are solid calcium carbonate biomineralisates in the inner ear and play an important role in hearing [1,2,3,4]
The p-a sensor measurements showed that the in phase condition resulted in higher sound pressure level (SPL) and lower particle acceleration levels (PALs) compared to the values yielded by the out of phase condition
Motion of auditory structures depends on sound pressure and particle motion The motion patterns of auditory structures in both species clearly differ when the shakers were driven in phase or out of phase
Summary
Otoliths of modern bony fishes (Teleostei) are solid calcium carbonate biomineralisates in the inner ear and play an important role in hearing [1,2,3,4]. Teleost otoliths show a tremendous diversity in morphology, especially with respect to shape [5,6,7,8]) Despite this known morphological diversity, it remains elusive how different otolith shapes affect sound-induced otolith motion and contribute to hearing in fish [4,9,10]. LS-2752, TSM, MH, FL); https://www.esrf.eu/ Bavaria California Technology Center The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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