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First published online December 14, 2006
Journal of Experimental Biology 210, 107-117 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.02634

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Feeding, fins and braking maneuvers: locomotion during prey capture in centrarchid fishes

Timothy E. Higham

Department of Organismic and Evolutionary Biology, Concord Field Station, Harvard University, 100 Old Causeway Road, Bedford, MA 01730, USA

View larger version (52K): [in this window] [in a new window]   Fig. 1. Representative photographs of a pectoral fin from bluegill (A) and largemouth bass (B). Both fins are from the left side of the animal. Note that bluegill exhibit a significantly higher (P<0.05) pectoral fin aspect ratio than largemouth bass (1.82 versus 1.34).

View larger version (56K): [in this window] [in a new window]   Fig. 2. Representative sequences for bluegill sunfish (A-C) and largemouth bass (D-F) decelerating during prey capture. The top two panels (A,D) are at 60 ms prior to maximum gape, the middle two panels (B,E) are at the time of maximum gape and the bottom two panels (C,F) are at 60 ms after maximum gape. Within each panel, the lateral view is above and the ventral view is below. The prey item is not shown because it is quite far in front of the fish 60 ms prior to maximum gape and it is inside the mouth at maximum gape and 60 ms after maximum gape. Note that the excursion of the pectoral fins is greater in largemouth bass than bluegill sunfish. Also note that both species employ their caudal, medial and pectoral fins during braking.

View larger version (24K): [in this window] [in a new window]   Fig. 3. Mean (± s.e.m.) swimming speeds (A) in 20 ms bins from 120 ms prior to maximum gape to 60 ms after maximum gape for bluegill sunfish (red circles) and largemouth bass (blue squares). The instantaneous value of speed was extracted at each time, rather than averaging the speed over the interval between bin durations. (B) Mean swimming speeds (± s.e.m.) shown in A scaled to the initial swimming speed 120 ms prior to maximum gape. Shaded areas indicate the time prior to maximum gape, and the unshaded areas indicate the time following maximum gape. Largemouth bass exhibit much higher swimming speeds prior to and during prey capture than do bluegill. While both species decelerate considerably following prey capture, largemouth bass exhibit a greater magnitude of deceleration. Note that, for both species, there is an increase in swimming speed immediately before maximum gape.

View larger version (5K): [in this window] [in a new window]   Fig. 4. Log-log plot of maximum gape versus ram speed (measured at the time of maximum gape), which is scaled to the ram speed 120 ms prior to maximum gape, for largemouth bass. Maximum gape during prey capture is positively correlated with ram speed (y=3.7719x-37.135; r2=0.58; P<0.001).

View larger version (27K): [in this window] [in a new window]   Fig. 5. Mean (± s.e.m.) pectoral (A) and anal (B) fin angles in 20 ms bins from 100 ms prior to maximum gape to 60 ms after maximum gape for bluegill sunfish (red circles) and largemouth bass (blue squares). Shaded areas indicate the time prior to maximum gape and unshaded areas indicate the time following maximum gape. Note that largemouth bass protract their pectoral fins more than bluegill during braking. Both species abduct their anal fins greatly after prey capture.

View larger version (16K): [in this window] [in a new window]   Fig. 6. Ram speed 120 ms prior to maximum gape versus average deceleration for 60 ms after maximum gape (A) and mean change in body angle along the z-axis for the final 80 ms of prey capture (20 ms prior to maximum gape plus 60 ms after maximum gape) (B) for bluegill sunfish (red circles) and largemouth bass (blue squares). Note that A is a log-log plot. For both bluegill (y=9.2776x-17.049; r2=0.43; P<0.0001) and largemouth bass (y=5.8397x+516.67; r2=0.31; P<0.01), an increase in ram speed 120 ms prior to maximum gape resulted in a significantly higher magnitude of deceleration following prey capture (A). For largemouth bass (y=0.1941x-11.158; r2=0.52; P<0.001), but not bluegill (y=0.0027x-0.4328; r2=0.005; P>0.5), an increase in ram speed 120 ms prior to maximum gape resulted in a greater change in body angle over the last 80 ms of prey capture (B).

View larger version (9K): [in this window] [in a new window]   Fig. 7. Results (factor scores) from a principal components analysis (PCA) using nine locomotor variables from bluegill sunfish (red circles) and largemouth bass (blue squares). The parentheses located at each axis indicate the variables in which loadings were >0.5. The negative signs indicate a negative loading. Note that largemouth bass and bluegill differed significantly with respect to PC 1 but not PC 2. PC 1 and PC 2 explained 33.6% and 20.8% of the total variance, respectively. See Table 3 for component loadings. Pecmax=maximum angle of the pectoral fin; Analmax=maximum angle of the anal fin; Caudmax=maximum angle of the caudal fin; BAz=angle of the body in the z-axis 60 ms after maximum gape; VMG=swimming velocity at maximum gape; tPec,max=time of maximum pectoral fin angle; Decavg=magnitude of deceleration averaged over the last 60 ms of prey capture.