Simple decision rules underlie collaborative hunting in yellow saddle goatfish.

Collaborative hunting, the coordination of animal behaviour in space and time to capture prey, is reported in several vertebrate species. However, previous studies are observational, hampering our ability to identify individual decision rules that result in collaboration. We experimentally investigated collaborative hunting in yellow saddle goatfish (Parupeneus cyclostomus) by exposing pairs to a mock prey that fled to an artificial shelter with multiple entrances. The first fish to initiate the chase (the 'initiator') was always closest to the prey and pursued it directly in its path. Conversely, the behaviour of the second goatfish (the 'follower') depended on its spatial position relative to the initiator. When the follower was less than one body length behind the initiator, it also accelerated directly towards the prey in over 95% of cases. However, if the two goatfish were separated by a distance of one body length or more, the follower chose a less direct route to reach the prey in 87% of cases. In this scenario, the follower often reached the prey's more distant refuge first, which might increase its hunting success or block the prey's escape path under natural conditions. Our findings suggest that coordinated hunting behaviour can result from simple, self-serving decisions.