Ear Development in Select Coral Reef Fishes: Clues for the Role of Hearing in Larval Orientation Behavior?

The pelagic larvae of coral reef fishes can detect and discriminate among different types of sounds suggesting that they may be able to localize acoustic cues and thus identify suitable settlement sites on reefs. It has been suggested that a description of ear development may provide clues about the importance of sound in larval behavior. Here we provide the first description of the ontogeny of the ear in the pelagic larvae and juveniles of representatives of three important families of coral reef fishes: Gobiidae (Elacatinus lori, E. colini), Apogonidae (Cheilodipterus quinquelineatus), and Pomacentridae (Amblyglyphidodon leucogaster, Amphiprion polymnus). Histological analysis revealed that the ear of the larvae and juveniles of the five study species lack any of the morphological specializations known in percomorph fishes. However, it showed that the ears of the two gobies are quite similar with respect to size and shape of the three otolithic organs, but that ears of the cardinalfish and damselfishes are different with respect to the absolute and relative sizes and position of the otolithic organs, as well as the timing of the appearance of the lagena; however, the functional significance of these features are unknown. It is concluded that if hearing plays a role in orientation behavior in the pelagic larvae of coral reef fishes then their "unremarkable'' ears are sufficient to allow these diminutive fishes to carry out the extraordinary feat of navigating the open ocean and successfully locating coral reefs on which to settle.