Influence of resonance-driven bubble clouds on fine-scale behaviour of common carp (Cyprinus carpio)

Acoustic-bubble barriers show potential as a management tool for fish passage. Although greater efforts are now being made to better understand the fundamentals that underpin reactions of fish to such barriers, the phenomenon of bubble coalescence has not yet been considered. When introducing air underwater smaller bubbles coalesce with successor bubbles at the orifice so that without vibration the bubble which enters the liquid is large. Orifice diameter has historically been used as a measure of bubble size, however as detachment and fragmentation occur unpredictably this method is unreliable, indicating insufficient control over the stimulus generated. This study used lower air flows (6 l min⁻¹ m⁻¹) and haptic feedback motors to vibrate the injection nozzles and reduce coalescence. Greater uniformity in bubble size allowed matching of the bubble population to a sound field to which the bubbles were resonant. In a proof-of-concept study, fish response to two resonant acoustic-bubble barriers was tested and compared to two non-resonant acoustic-bubble walls. The scattering and absorption coefficients for all segments of the bubble population were calculated to determine the most important bubble sizes for attenuation. Analysis of fish movement and orientation was used to examine fish behaviour in relation to the sound fields generated.