Sound production and hearing in coral reef butterflyfishes.

Abstract

Butterflyfishes (family Chaetodontidae) exhibit a diversity of close affiliative social behaviors. All 87 species of Chaetodon have a laterophysic connection and extensions of the anterior horns of the swim bladder near the otic capsule, which are proposed to impart sound pressure sensitivity to the normally mechanosensitive lateral line and acceleration‐sensitive inner ear. Video kinematic analyses reveal that the motor action patterns used to produce pulsed sounds vary among species. The sound production mechanisms in Chaetodon and Forcipiger do not appear to be conserved, thus sound production may have evolved independently within the family. Species with long swim bladder horns have lower AEP hearing thresholds than those without, and deflation of the horns and bladder decreases hearing sensitivity in the former group. When the laterophysic connection and swim bladder horns are physically disrupted in wild fish, movement within their territories decreases and fish pairs swim closer together. Thus, the low intensity sounds produced by butterflyfishes may favor close social behaviors that increase communication efficiency among individuals on a noisy coral reef. We are currently investigating how hydrodynamic flow fields produced during social interactions may be used for intraspecific communication during these natural behaviors.