Swimbladder acoustic pressure transduction initiates Mauthner-mediated escape

Abstract

THE bilateral Mauthner neurons initiate the characteristic 'C-start'1,2 escape of fishes when they respond to underwater sounds accompanying attacks by predators3–6. Either of the two sound components, particle motion or pressure change can initiate Mauthner-mediated escape. Particle motion can be detected by inner ear sensory receptors and used for locating a sound source7, but sound pressure requires a transduction mechanism to stimulate the same receptors8–10. For fishes, sound pressure is a nondirec-tional scalar signal that is transduced by the swimbladder11,12. It might be assumed that particle motion, because of its directional nature, triggers Mauthner-initiated predator evasion2, but we demonstrate here that for acoustically mediated escape, sound pressure is the salient stimulus for activating the Mauthner neurons in fishes with swimbladders. This implies that displacement determines which of the two Mauthner neurons is activated, so that the fish turns away from the direction of the predatory attack.