Reef fish escape responses selectively match predator attack speeds.

Abstract

Animals must continually balance foraging with the risk of predation. In complex natural environments, this means quickly distinguishing between threats and harmless situations. We investigated how site-associated coral reef fishes escape in response to visual cues mimicking predator attacks, using controlled underwater presentations of looming stimuli at varying speeds. We measured escape responses across species and social contexts, and compared them to predator attack speeds observed in the same habitat. Escape probability increased sharply with the speed of the looming stimulus, with no responses at low speeds. Stimulus speeds that triggered escape responses matched those of predator attacks, whereas speeds similar to those of cruising predators never triggered a response. The two species differed in behavior: Brown Chromis ranged farther from shelter and responded more readily, whereas Bicolor Damselfish stayed close to shelter and responded less. Contrary to expectations, social context did not affect responses. These findings demonstrate that reef fish are highly sensitive to the approach speed of objects, with species-specific behavior further shaping their responses. By combining realistic visual threats with natural predator attack data, this study offers insight into how animals make rapid escape decisions in complex, real-world environments.