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First published online June 29, 2006
Journal of Experimental Biology 209, 2713-2725 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02315

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Multidimensional analysis of suction feeding performance in fishes: fluid speed, acceleration, strike accuracy and the ingested volume of water

Timothy E. Higham^1,*, Steven W. Day² and Peter C. Wainwright¹

¹ Section of Evolution and Ecology, University of California, One Shields Avenue, Davis, CA 95616, USA
² Department of Mechanical Engineering, Rochester Institute of Technology, 76 Lomb Memorial Drive, Rochester, NY 14623-5604, USA

View larger version (29K): [in a new window]   Fig. 1. A schematic diagram of the measurements made to characterize strike accuracy. The boundary, which surrounds the ingested volume of water in lateral view, shows a typical shape for a largemouth bass (dark line). The lighter boundary shows a typical shape of the ingested volume of water for a bluegill sunfish. The aspect ratio of the parcel of ingested water was calculated from its length and height. Strike accuracy was determined by measuring the distance from the center of the parcel (COP) to the center of mass of the prey (COM) and then dividing this by the distance between the COP and the boundary of the ingested volume, intersecting the COM of the prey. The vertical (Ay) and horizontal (Ax) components of accuracy were determined by measuring the distance between the COM of the prey and each axis.

View larger version (17K): [in a new window]   Fig. 2. Time to peak gape (TTPG) versus fluid speed for both bluegill sunfish (black circles) and largemouth bass (red triangles) using fluids speeds calculated in the earthbound frame of reference (A) and the fish's frame of reference (B). The curve in A is fit to the bluegill sunfish data to show how largemouth bass exhibit a similar relationship. For both species, fluid speed (measured at peak gape in front of the fish on the center line) increases with a decrease in TTPG. Note that the variation in fluid speed for a given TTPG is higher for bass than bluegill in both A and B. Also note that the variation in fluid speed for a given TTPG is much greater when accounting for the ram speed of the fish (B). The data for bluegill are from Day et al. (Day et al., 2005).

View larger version (16K): [in a new window]   Fig. 3. Mean profiles of scaled speed along the centerline transect for bluegill sunfish (black circles) and largemouth bass (red triangles). The lines correspond to the polynomial fit to each pooled dataset. For each feeding in these pooled datasets, the profile at the time of peak fluid speed was scaled by dividing spatial distances by gape at this time and the magnitude of speed by the measured speed located at a distance of gape in front of the fish. The speed at this location is used throughout as a reference, because at this location fluid speed is substantial and the PIV measurements meet the validation criteria (see Materials and methods). The error bars represent the s.d. of the residuals about the fit lines. Fluid speed at the mouth aperture is approximately 3.5 times (bluegill) and 4.5 times (bass) that at gape. The data for bluegill are from Day et al. (Day et al., 2005).

View larger version (36K): [in a new window]   Fig. 4. Representative sequences of gape (black circles), volume (red squares), fluid speed in the earthbound frame of reference (green upward triangles), and the change in volume per unit time (dV/dt; blue downward triangles) for (A) largemouth bass and (B) bluegill sunfish. Positive values of fluid speed indicate that the water is flowing towards the fish's mouth. Note that the volume ingested by largemouth bass is substantially greater than the volume ingested by bluegill sunfish. Also note that maximum gape of largemouth bass is approximately twice that of bluegill. For this figure, we applied a smoothing spline with a smoothing factor of 1 or 2 to each of the variables using Igor Pro 5.01 (WaveMetrics Inc., Lake Oswego, OR, USA).

View larger version (15K): [in a new window]   Fig. 5. Relative timing of kinematic events and peak fluid speeds for bluegill (top) and bass (bottom). To account for variation in absolute speed of the event, all times are shown normalized to TTPG. Because of the definition of TTPG used (see Materials and methods), the kinematic events of 20% PG and 95% PG are necessarily located at 0 and 1, respectively. All other symbols and error bars show the mean ± s.e.m. for all feedings analyzed. Note that peak fluid speed occurs at approximately the same time as 95% mouth opening for bluegill, but slightly after 95% opening for bass. Events that have some duration (duration of gape and prey entering) are represented as filled bars with error bars to show the s.e.m. for the start and finish of these events. The three values of the time of peak fluid speed (FS) represent three locations in front of the mouth of the fish relative to peak gape (PG). The data for bluegill are from Day et al. (Day et al., 2005).

View larger version (11K): [in a new window]   Fig. 6. Log-log plot of peak gape (PG; cm) versus (A) volume (V; mm3) and (B) the change in V per unit time t (dV/dt; mm3 s-1) for bluegill sunfish (circles) and largemouth bass (triangles). PG had a significant effect on V for both bluegill (r2=0.63; P<0.01) and bass (r2=0.67; P<0.01). Additionally, peak gape affected maximum dV/dt for both bluegill (r2=0.74; P<0.01) and bass (r2=0.67; P<0.01).

View larger version (12K): [in a new window]   Fig. 7. A log-log plot of time to peak gape (TTPG; ms) versus (A) volume (V; mm3) and (B) the change in volume per unit time (dV/dt; mm3 s-1) for bluegill sunfish (circles) and largemouth bass (triangles). TTPG did not affect V significantly in bluegill (r2=0.02; P=0.6) or bass (r2=0.19; P=0.06). Additionally, TTPG was significantly negatively related to maximum dV/dt in bluegill (r2=0.45; P<0.01) but not bass (r2=0.25; P=0.08).

View larger version (12K): [in a new window]   Fig. 8. A log-log plot of ram speed (cm s-1) versus ingested volume (V; mm3) for bluegill sunfish (circles) and largemouth bass (triangles). Ram speed significantly affected ingested volume for bluegill (r2=0.27; P=0.03) and bass (r2=0.26; P=0.03).

View larger version (12K): [in a new window]   Fig. 9. A plot of ram speed versus the height to length ratio of the ingested volume of water for largemouth bass. As ram speed increased, the ingested volume of water became significantly more elongate and narrow (r2=0.57; P<0.01). This relationship, showing a similar trend, is published elsewhere for bluegill sunfish (Higham et al., 2005a).

View larger version (13K): [in a new window]   Fig. 10. (A) Plot of ram speed versus the accuracy index (AI) for largemouth bass (triangles) and bluegill sunfish (circles). Note that bluegill were more accurate than largemouth bass but that accuracy did not decrease significantly with ram speed for either species. (B) Graph of horizontal (black bars) and vertical (gray bars) accuracy for largemouth bass and bluegill sunfish. Note that bluegill sunfish were significantly more accurate than largemouth bass in the vertical plane (P<0.01) but not the horizontal plane.

View larger version (16K): [in a new window]   Fig. 11. Plots of (A) peak fluid speed versus peak acceleration, and (B) accuracy versus the volumetric flow rate, for largemouth bass (triangles) and bluegill sunfish (circles). In A, the red symbols indicate measures of peak fluid speed and acceleration in the fish's frame of reference (FF), whereas the black symbols indicate values in the earthbound frame of reference (EF). Peak fluid speed, peak acceleration and volumetric flow rate (dV/dt) were calculated using the single maximum value for each variable for each individual. Thus, each point represents the single highest value for each individual. Accuracy was calculated by selecting the three sequences per individual that had the highest peak fluid speed and then averaging the accuracy for those three strikes.