Intentional communication in a fish (#57)
Intentional communication–where the sender has a goal for the recipient’s behaviour–is distinguished from communication governed by automatic responses by at least eight behavioural criteria know as the hallmarks of intentionality. The more hallmarks possessed, the stronger the evidence for intentionality. Apes are currently the only non-human species demonstrated to possess all the hallmarks, while some other large brained species possess a subset. Smaller brained species have been largely overlooked, with the exception of fish of the genus Plectropomus. Observations in the wild demonstrate that they exhibit some hallmarks of intentionality in their communication with moray eel collaborative hunting partners. Here, we use a series of aquaria experiments to investigate intentional communication by the leopard coral grouper Plectropomus leopardus from the Great Barrier Reef. We find that it tailors its communication to the moray’s attentional state, and has a goal for the moray’s behaviour with respect to a hidden prey item, strategically altering its behaviour based on the moray’s reactions to its signals. In conjunction with previous observational evidence, our results show that plectropomid fish exhibit the hallmarks of intentionality to a comparable level to apes. Thus a relatively small brain does not prohibit these fish from possessing this complex cognitive process, adding an important piece to the puzzle of its evolutionary origins.