Tomographic imaging using an experimental standing wave tube-like setup to explore moving fish hearing structures

Modern bony fishes show significant variation in the morphology of their hearing structures, which have been studied for almost two centuries. However, the exact processes of sound transmission, interaction, and their contributions to fish hearing are still matters of assumption. Characterizing the sound-induced in situ motion of fish auditory structures and their interplay while avoiding invasive damage is very challenging. A new synchrotron radiation-based tomography setup characterizes the motion of these structures (swimbladder, auditory ossicles, inner ear otoliths), allowing in situ morphofunctional studies with unprecedented resolution. We developed a miniature standing wave tube to meet the needs of tomography and tank acoustics, enabling control over the acoustic field. Sound Pressure Levels can be determined and adjusted during tomographic measurements, generating sound pressure or sound-induced particle motion at the test subject, and the setup reliably produces frequencies of up to 2 kHz. We tested six otophysan species, including the glass catfish (Kryptopterus vitreolus) and zebrafish (Danio rerio), and were able to visualize the dynamic interactions and movements of fish auditory structures in response to pure tone stimuli. Our approach will enhance our understanding of fish sound detection and set a new standard for non-invasive, high-resolution imaging techniques in the field of aquatic sensory biology.