FERRY-GRAHAM, L.A.; WAINWRIGHT, P.C.; LAUDER, G.V.: Sources of fluid flow during feeding in bluegill sunfish as identified using DPIV

Two key predictions of the fluid mechanics literature have never been tested empirically in suction feeding fishes. First, it is expected that the velocity of flow into the mouth during buccal expansion will decrease exponentially with distance from the mouth. Second, forward movement of the predator during the strike should push water toward the prey, diminishing the effect of suction generation and the net flow of water into the mouth of the predator. We used Digital Particle Image Velocimetry and 500 Hz video to quantify the pattern of water flow around the head of feeding bluegill sunfish. During the strike peak water velocity averaged 6 cm/s and occurred just prior to maximum gape, as the prey entered the mouth. A detailed spatial analysis of flow at this time point revealed that velocity increased with distance directly in front of the mouth, until about 0.5 cm after which velocity decreased exponentially with distance. Forward body velocity was correlated with the distance from the mouth at which peak suction flow occurred. This pattern is consistent with the idea that the suction flow interacts with water being displaced by the forward moving fish.