HIGHAM, T.E.; DAY, S.W.; WAINWRIGHT, P.C.; Univ. of California, Davis; Univ. of California, Davis; Univ. of California, Davis: The effects of swimming speed on suction feeding in bluegill sunfish: flow quantification using Particle Image Velocimetry

It is well established that suction feeding fish use a variable amount of swimming (ram) during prey capture. However, the fluid mechanical effects of ram on suction performance have not been established. Suction performance can be measured as the maximum velocity of the water entering the mouth during feeding. Thus, for different ram speeds, we quantified the patterns of water flow entering the mouth of bluegill sunfish (Lepomis macrochirus) while feeding. Using Particle Image Velocimetry and high-speed video, we observed the flow in front of the mouth of the fish using a vertical laser sheet positioned on the mid-saggital plane of the fish. Ram speed, measured at the time of maximum gape, ranged between 0 and 18 cm/s. The average peak suction flow speed in 36 feedings ranged from 15 to 55 cm/s (average of 32 cm/s), measured approximately half a mouth diameter in front of the fish. At the mouth opening, the flow speed ranged from 30 to 110 cm/s (average of 64 cm/s). After correcting for kinematics, the peak flow speed toward the mouth showed a tendency to be slightly higher when ram speed was low, but this difference was not statistically significant. This small difference indicates a surprisingly subtle effect of ram on suction flows. The implication of this finding is that suction feeders that employ ram of around 10-20% of suction speeds sacrifice little in terms of the flow speeds they generate and that ram speed enhances the total closing speed of the predator. Supported by NSF IBN-0326968.