Data from: Fish prey change strategy with the direction of a threat

Predation is a fundamental interaction between species, yet it is unclear what escape strategies allow prey to survive. Classical theory proposes that prey should either escape in a direction that conforms to a performance optimum or is random and therefore unpredictable. Here we show that larval zebrafish (Danio rerio) instead employ a mixed strategy that depends on the direction of a predator's approach. This was determined by testing classic theory with measurements of escape direction in response to a predator robot. We found that prey consistently responded to a predator with a contralateral escape response when the robot approached from a lateral direction, where they appeared at a central position in the prey's visual field. This response was consistent with an escape strategy that maximizes the distance from the predator. In contrast, when the robot approached the rostral or caudal end of the body, prey responded with an equal probability of a contralateral or ipsilateral response. These randomly-directed responses were elicited when the prey was aligned with the predator's heading. At such an orientation, here is little advantage to a contralateral response and the predator appears in the peripheral vision of the prey. Therefore, the mixed strategy of larval zebrafish is optimal when strategically beneficial and is otherwise random, with the response stimulated by the predator's position in the prey's visual field. This sensory-mediated mixed strategy offers a new paradigm for understanding the factors that govern prey survival.