DAY, S.W.*; HIGHAM, T.E.; CHEER, A.Y.; WAINWRIGHT, P.C.; Univ. of California, Davis: Spatial and Temporal Flow Patterns during Suction Feeding of Bluegill by Particle Image Velocimetry

The suction feeding fish generates a flow field external to its head that draws the prey towards the mouth. To date there are very few empirical measurements that characterize the fluid mechanics of suction feeding, particularly the temporal and spatial patterns of velocity and pressure of water in front of the fish. To characterize the flow in front of suction feeding bluegill (Lepomis macrochirus), measurements with high spatial (<1mm) and temporal (500 Hz) resolution were made with Particle Image Velocimetry (PIV) (3 individuals, 45 feedings). A novel method of tracking individual seed particles was also used to determine the parcel of water that the fish ingests. A Computational Fluid Dynamics (CFD) model, which calculates pressure everywhere in the flow and can be used for parametric studies with relative ease, was used to complement the measurements. PIV and particle tracking show that water is drawn from all around the mouth. Fluid velocity decreases exponentially with distance from the mouth and is only significant (>5% mouth speed) within roughly 1 mouth diameter (D) of the fish. CFD shows that generated suction pressure decays even more quickly than velocity, increasing to within 5% of ambient at 0.5 D. CFD parametric studies also exhibit similarity of flows for varying combinations of ram, suction, and mouth size, suggesting some generality of the empirical results. Comparison of time resolved fluid velocity measurements at a constant distance in front of the fish (5 mm, 0.5 D) to gape kinematics shows that peak fluid speed occurs at about 80% of peak gape. The magnitude of peak fluid speed during each strike decreases as a function of time to peak gape (R²=0.87), demonstrating a relationship between kinematics and fluid dynamics. Supported by NSF IBN-0326968.