Relationship between jaw morphology, bite performance and diet in Serrasalmidae (Characiformes, Teleostei)

Serrasalmidae are mainly known for “piranhas” and their negative reputation of ferocious predatory fishes. A recent study demonstrated that the piranha $Serrasalmus rhombeus£ had an extreme bite force that is even proportionally greater than that of the white shark. However, these sharp teeth fishes represent only a minority of Serrasalmidae. Other serrasalmid species (pacus and myleus) feed on plants, fruits or seeds and their bite force and feeding capacities are still uninvestigated. In the present research, in vivo bite forces were measured and compared according to jaw morphology in ten species of Serrasalmidae including six herbivorous and four carnivorous species. The Bite Force Quotient (BFQ) was calculated for each individual to compare the jaw strength across species. The results of the analysis showed that species feeding on fins and fish flesh have a significant greater bite force than species feeding on plants, fruits or seeds. This difference can be explained by the larger adductor mandibulae muscle in carnivorous species which have comparatively longer and higher skull than herbivorous species. In addition, there is a significant difference in the lower jaw morphology between piranhas and pacus and relatives. The piranha species have longer lower jaws than pacus and myleus species which have shorter and higher lower jaws. This study shows that the Serrasalmidae family regroups remarkable biters whose bite performance is mostly related to diet.