DAY, S W*; HIGHAM, T E; WAINWRIGHT, P C; Rochester Institute of Technology; Univ. of California, Davis; Univ. of California, Davis: THE RELATION OF SUCTION PRESSURE AND FLUID SPEED DURING FEEDING IN LARGEMOUTH BASS

The suction feeding fish simultaneously generates negative pressure within the mouth and a flow field external to its head that draws prey towards the mouth. In the literature, both pressure within the mouth and fluid speed in front of the fish have been alternatively modeled and/or measured and used as indicators of performance. Conflicting arguments have been made about the relationship between pressure and fluid speed and whether one can serve as a proxy for the other. Can this relationship be explained by the Bernoulli equation or is this model invalidated by unsteady effects and complexity of the flow? We have attempted to address this question directly by simultaneously measuring fluid speed, using particle image velocimetry, and buccal cavity pressure in a largemouth bass (Micropterus salmoides) eating evasive ghost shrimp. For each feeding, we calculated an expected pressure in the mouth as a function of time by applying both steady and unsteady forms of the Bernoulli equation to the measured velocity field. Measured peak buccal pressures always occurred before peak fluid speed, and therefore earlier than peak pressures predicted by the steady form of the Bernoulli equation. Predictions of pressure that include the unsteady terms in the Bernoulli equation resolve this discrepancy and lead to good agreement in the time of peak fluid speed. Measured pressures have a considerably larger magnitude (approximately two times) than those predicted by either form of the Bernoulli equation during the expansive phase of the gape, but agree fairly well during peak gape and closing. This indicates that some amount of generated pressure is not related to fluid velocity or acceleration, but energy dissipated by fluid mechanical losses. Supported by NSF IOB-0444554