Functional groups in piscivorous fishes

Piscivory is a key ecological function in aquatic ecosystems, mediating energy flow within trophic networks. However, our understanding of the nature of piscivory is limited; we currently lack an empirical assessment of the dynamics of prey capture, and how this differs between piscivores. We therefore conducted aquarium-based performance experiments, to test the feeding abilities of 19 piscivorous fish species. We quantified their feeding morphology, striking, capturing, and processing behaviour. We identify two major functional groups: grabbers and engulfers. Grabbers are characterised by horizontal, long-distance strikes, capturing their prey tail first, and subsequently processing their prey using their oral jaw teeth. Engulfers strike from short distances, from high angles above or below their prey, engulfing their prey, and swallowing their prey whole. Based on a meta-analysis of 2,209 published in situ predator-prey relationships in marine and freshwater aquatic environments, we show resource partitioning between grabbers and engulfers, with grabbers feeding on relatively larger prey than engulfers. Our results provide a functional classification for piscivorous fishes, delineating patterns which transcend habitats, that may help explain size structures in fish communities.