Hearing capacities and morphology of the auditory system in Serrasalmidae (Teleostei: Otophysi).

Like all otophysan fishes, serrasalmids (piranhas and relatives) possess a Weberian apparatus that improves their hearing capacities. We compared the hearing abilities among eight species of serrasalmids having different life-history traits: herbivorous vs. carnivorous and vocal vs. mute species. We also made 3D reconstructions of the auditory system to detect potential morphological variations associated with hearing ability. The hearing structures were similar in overall shape and position. All the species hear in the same frequency range and only slight differences were found in hearing thresholds. The eight species have their range of best hearing in the lower frequencies (50-900 Hz). In vocal serrasalmids, the range of best hearing covers the frequency spectrum of their sounds. However, the broad overlap in hearing thresholds among species having different life-history traits (herbivorous vs. carnivorous and vocal vs. non-vocal species) suggests that hearing ability is likely not related to the capacity to emit acoustic signals or to the diet, i.e. the ability to detect sounds is not associated with a given kind of food. The inner ear appears to be highly conservative in this group suggesting that it is shaped by phylogenetic history or by other kinds of constraints such as predator avoidance.