Meeting Abstract

51.5  Monday, Jan. 5  Tuned to the right signal: Suction feeding interactions with bow wave increase detection distance of fish by aquatic prey HOLZMAN, Roi*; WAINWRIGHT, Peter; Univ. of California, Davis; Univ. of California, Davis raholzman@ucdavis.edu

Predation on zooplankton by fish is a major trophic pathway in aquatic communities, and this predator-prey interaction represents a challenging encounter for both prey and predator. To capture the prey by suction feeding, a fish must get sufficiently close to the prey, rapidly open its mouth and expand its buccal cavity to draw the water and the prey towards it. Both the swimming towards the prey and the suction flows create a hydrodynamic disturbance, which can elicit an escape response by the prey. However the hydrodynamic disturbance generated by suction feeding fishes was previously assumed to result exclusively from the bow wave produced by the swimming fish. Using Particle Image Velocimetry (PIV) we directly measured flow speeds and strain rate at the location of the prey through the fish’s approach, and compared those measurements to the flow speeds and strain rates that are due to swimming alone, as measured at an upstream point. At the prey, water was first pushed away from the fish due to the bow wave but later flow speed reversed due to suction, while at the upstream point water was only pushed away from the fish. The velocity magnitude of flow was similar between the two sampling points. However, strain rate, a measure of fluid deformation that is a proxy for copepod escape responses, was 3 times higher at the location of the prey due to the opposing forces of the bow wave and suction flow. By inference, the distance at which an escape response of a copepod is initiated was ~30% longer at the prey, due to the interaction of the bow wave and suction flows. Sensory tuning to strain rate, rater than velocity magnitude, seems to be an important adaptation to fish avoidance in zooplankton.