In humans, referential gestures intentionally draw the attention of a partner to an object ofmutual interest, and are considered a key element in language development. Outside humans,referential gestures have only been attributed to great apes and, most recently, ravens. Thiswas interpreted as further evidence for the comparable cognitive abilities of primates andcorvids. Here we describe a signal that coral reef fishes, the grouper Plectropomus pessuliferusmarisrubri and coral trout Plectropomus leopardus, use to indicate hidden prey to cooperativehunting partners, including giant moray eels Gymnothorax javanicus, Napoleon wrassesChelinus undulatus and octopuses Octopus cyanea. We provide evidence that the signalpossesses the five attributes proposed to infer a referential gesture: it is directed towards anobject, mechanically ineffective, directed towards a potential recipient, receives a voluntaryresponse and demonstrates hallmarks of intentionality. Thus, referential gesture use is notrestricted to large-brained vertebrates.
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