HIGHAM, T. E.*; DAY, S. W.; WAINWRIGHT, P. C.; Univ. of California, Davis; Rochester Institute of Technology; Univ. of California, Davis: Can peak buccal cavity pressure be used to predict peak fluid speed during suction feeding in fishes?

Suction-feeding fish capture prey by rapidly expanding their buccal cavity, which generates a flow of water directed towards their mouth. A sub-ambient pressure inside the buccal cavity is associated with this expansion, and the magnitude of this pressure differs considerably among species of fish and within an individual. Although peak sub-ambient pressure is thought to be proportional to fluid speed squared by Bernoulli�s principle, no study has measured both pressure and fluid speed simultaneously. Thus, we quantified buccal pressure and fluid speed simultaneously during feeding in four individuals of largemouth bass, Micropterus salmoides. We measured pressure by inserting a transducer through the skull of the fish so that the tip of the transducer was flush with the dorsal surface of the buccal cavity. We measured fluid speed using digital particle image velocimetry (DPIV). A laser sheet was positioned on the mid-sagittal plane of the fish so that the fluid speed could be measured along a transect extending from the center of the fish�s mouth. We found that peak pressure was significantly correlated with the peak fluid speed (r²=0.61; P<0.01) of the same feeding. However, the magnitudes of the pressures were much greater (up to 5 times) than those estimated from the measured fluid speeds. We found that peak pressure preceded peak gape and peak fluid speed by an average of 14 ms and 18 ms, respectively. Thus, although correlated, pressure is sub-maximal at the time of peak fluid speed. In conclusion, a substantial amount of variation in peak fluid speed cannot be explained by peak pressure, suggesting that a mechanism other than pressure is being modulated by the fish in order to alter fluid speed. Supported by NSF IOB-0444554.