Sound production mechanism in Amphiprion clarkii (Teleostei: Pomacentridae)

In the family Pomacentridae, six genera were reported as sound producers: Amphiprion, Dascyllus, Stegastes, Chromis, Abudefduf and Plectroglyphidodon. The anemonefishes (Amphiprioninae) live in social group in association with sea anemones, which protect them from predators. Their sound emissions seem involved in courtship and territorial defense, contributing to both survival and reproductive success. However, the mechanism of sound production is unresolved. It has been hypothesized that it involves swimbladder or the action of the pharyngeal jaws amplified by swimbladder. The aim of this study was to understand the sonic mechanism involved in the agonistic sounds in Amphiprion clarkii. The approach consists in high-speed cineradiography and functional morphology. During agonistic sounds (pops), fishes perform different movements such as skull elevation, pectoral girdle retraction, hyoid lowering and mouth closing. Pops are produced when the hyoid is completely lowered and the mouth closed. The simultaneous realization of these movements was never observed in teleost. In Amphiprion sp., it is possible due to an additional ligament inserted on the hyoid bar and on the inner lower jaw. The hyoid lowering combined to the closing (and thus the elevation) of the mandible could generate a tension of the ligament, provoking its vibratio