Fig. 4. Measured values of peak fluid speed (cm s^-1) and peak buccal pressure (kPa) for largemouth bass (black upward triangles) and bluegill sunfish (red squares), and the fluid speeds predicted from the model (Muller et al., 1982) for largemouth bass (black downward triangles) and bluegill sunfish (red circles). As in previous plots, the absolute value of buccal pressure is shown. The lines designated as `model' are based on values of peak fluid speed calculated using the model (Muller et al., 1982) for the pressures that we measured. This was done separately for each species. See text for additional explanations. The slopes of the linear regressions fit to the model output (0.51) are higher than the slopes of the empirical data for largemouth bass (0.36) and bluegill sunfish (0.38), and the values for fluid speed predicted by the model are well above the measured values. Note that pressure explains more of the variation in fluid speed for bluegill (r²=0.79; P<0.001) than bass (r²=0.56; P<0.001). (A) Fluid speeds where we measured them are shown, at a distance equal to peak gape away from the mouth aperture; (B) fluid speeds at the mouth aperture. In order to transform the measured values of fluid speed to values at the mouth aperture, we multiplied the bass values by 4.6 (Higham et al., 2006) and the bluegill values by 3.6 (Day et al., 2005), based on empirical relationships of the drop in fluid speed with distance from the mouth aperture. Note that the two species exhibit different relationships between pressure and fluid speed for fluid speeds measured at the mouth aperture, whereas the two species are similar for fluid speeds measured at peak gape away from the mouth.