The evolutionary success of otophysans, a major lineage of fish diversity, is often attributed to a novel morphology involving unique bones, anterior vertebrae, and the swim bladder. This feature, termed the Weberian apparatus (WA), is an accessory hearing organ that transduces sound from the swim bladder to the inner ear. As a result, otophysans have sensitive hearing, however, the adaptive function for such ability is unknown. Further, the effect of WA morphological variation between species is not clear. It is hypothesized that acute hearing facilitates prey detection. This research will test this hypothesis by examining WA morphology and function in Serrasalmidae, an ecologically diverse otophysan family with 15 genera and ~60 species that include piranhas and pacus. Among serrasalmids are species that eat small fishes, scales off other fishes, small invertebrates, and falling fruits. The objectives of this research are to examine WA morphology in serrasalmids, to determine if morphology is related to hearing ability, and to test if prey can be localized by acoustic cues. This research will utilize the Muséum National de Histoire Nationelle specimen collection along with computerized tomography (CT), 3D imaging, and comparative analysis. Electrophysiology will be used to test hearing and behavioral experiments will examine piranha and pacu responses to prey sounds. This project will involve training in CT and 3D visualization, histological and microscopy methods, phylogenetic comparative analysis, and biomechanical modeling. The fellowship is expected to help the candidate realize an academic career. The candidate will learn cutting edge methods, develop skills for managing data, and gain experience with scientific presentations, writing and publishing. The unique opportunity to work with an internationally renowned research community and a highly respected functional morphology expert will allow the applicant to focus on a new, related research area.