First published online October 7, 2008
Journal of Experimental Biology 211, 3296-3305 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.020909
Integrating the determinants of suction feeding performance in centrarchid fishes
Roi Holzman1,*,
Steven W. Day2,
Rita S. Mehta1 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, USA
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Fig. 1. Representative profiles of gape kinematics (open diamonds), the distance
between the center of the predator's mouth and the prey (grey triangles), and
the force exerted on the prey (closed circles) in largemouth bass (A) and
bluegill (B). In largemouth bass, the distance between the predator and the
prey is closed by swimming towards the prey from a distance. In bluegill, that
distance is closed through jaw protrusion after a period of minimal ram (time
0–20 ms in B). Shaded area represents negative predator–prey
distance, i.e. the prey is in the mouth. Note the different force scale in A
and B.
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Fig. 2. Observed kinematic variation of largemouth bass (red bars; N=4
fish, 6–10 trials per fish) and bluegill sunfish (blue bars;
N=4 fish, 15 trials per fish) while striking on attached prey. The
two species were significantly different in their time to peak gape (A, TTPG)
and mouth displacement speeds (C) (repeated-measures ANOVA; P>0.05
for both) but strike initiation distance (B) and maximal gape diameter (D) did
not differ significantly (repeated-measures ANOVA; P<0.1 for
both).
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Fig. 3. The magnitude of peak force exerted on attached prey by largemouth bass
(red bars; N=4 fish, 6–10 trials per fish; total N=33)
and bluegill sunfish (blue bars; N=4 fish, 15 trials per fish; total
N=60). The force measured for bluegill (0.16±0.017 N); was
much higher than the force measured for bass (0.03±0.003 N;
repeated-measures ANOVA, P<0.001). The difference in force was
partly because bluegill's strike had, on average, twofold faster flow speeds
and accelerations [estimated based on the relationship between TTPG and flow
speed (Higham et al.,
2006 )].
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Fig. 4. Interspecific differences in the measured force exerted on attached prey.
To take into account the intraspecific variation in the acceleration at the
mouth aperture, we regressed the measured force against acceleration at the
mouth and then compared the slopes for the two species. Similar slopes (and
intercepts) would indicate that the differences in observed force are due to
differences in the acceleration at the mouth alone. However, the slope of the
regression was significantly different between species (mixed-effects model,
P<0.05), indicating a contribution of other factors to the
difference in force. Forces exerted by bluegill (BG) are indicated by blue
open circles and blue regression lines, largemouth bass data are indicated by
red open circles and red broken regression lines. Grey background represents
the observed range of accelerations at the mouth for bass.
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Fig. 5. Comparison of timing and magnitude of the observed and calculated forces
exerted by largemouth bass on tethered prey. Time 0 (A) is the first frame
digitized in the image sequence ( 10 frames prior to the onset of gape,
arbitrarily selected for each sequence). The timings of the observed and
calculated peak force were linearly correlated (mixed-effects model,
R2=0.659; F1,23=50.6,
P<0.001), with the timing for observed peak force preceding that
of the expected force (slope=0.66). Similarly, the peak calculated force was
correlated with the observed one (mixed-effects model,
R2=0.68; F1,23=55.74,
P<0.001) and a slope of 1.02 (B). Different symbols represent data
for the four fish studied, diagonal line represents the case of
x=y.
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Fig. 6. The effects of discrete kinematic variables on the force exerted on the
prey in a representative bass strike, illustrated using the force model.
Firstly, the force model was first run with the observed kinematics, returning
the expected force as a function of time (A). Peak force was recorded and the
maximal gape was than changed to fit the mean bluegill gape, force was
recalculated (B) and peak force recorded. Next, we changed strike initiation
distance to increase strike efficiency (C) and finally we changed mouth
displacement speed to fit the mean bluegill speed (D). The procedure
(A–D) was repeated for each strike and peak force was recorded following
each change. Note that changes to kinematics are cumulative so that each model
retains the changes made previously. Each change to kinematics appears in bold
font when first made.
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© The Company of Biologists Ltd 2008
