First published online September 14, 2007
Journal of Experimental Biology 210, 3328-3336 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.008292
Timing is everything: coordination of strike kinematics affects the force exerted by suction feeding fish on attached prey
Roi Holzman1,*,
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
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Fig. 1. Photograph of a bluegill striking at a tethered shrimp. The picture was
taken at time of peak gape (95% of maximal gape). The shrimp was glued to a
thin metal rod that was extended from a load cell (shown as a black oval) that
recorded data at 5000 Hz. Synchronized video recordings were made at 500
Hz.
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Fig. 2. (A) The change in observed force (filled circles), gape size (open
diamonds) and distance to the prey (gray triangles) during a representative
strike. The distance between the prey and the fish is closed by rapid forward
movement of the jaws that occurs during mouth opening. Note that the
initiation and peak of force lag the onset and peak of gape expansion,
respectively. Grey area represents negative distances, i.e. where the prey is
in the fish's mouth. (B) Temporal patterns for the force exerted on shrimp
prey by bluegill sunfish. Time is given as a fraction of TTPG, defined as the
duration from 20% to 95% of peak gape (0 to 1, respectively). The boxes have
vertical lines at the lower quartile, median and upper quartile values.
Whiskers represent the range for 95% of the observed values. N=48
strikes, 12 per fish.
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Fig. 3. The force exerted on attached shrimp as a function of TTPG (the speed of
buccal expansion). Note that for a given strike effort (TTPG) there is
considerable variation in force. The relationship between the observed force
and TTPG is given by the equation: peak observed
force=2.35xTTPG–1–0.05
(R2=0.42; solid line).
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Fig. 4. Variability in prey capture kinematics in bluegill striking tethered
shrimp. (A) Time to peak gape (TTPG); (B) strike initiation distance; (C)
mouth displacement; (D) maximal gape width. N=48 strikes, 12 per
fish. Strike initiation distance and mouth displacement were correlated
(R2=0.62, P<0.001) while no correspondence was
found between the other variables.
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Fig. 5. Comparison of timing (A) and magnitude (B) of the observed and calculated
forces exerted by bluegill on tethered prey. Time 0 (in B) is the first frame
digitized in the image sequence ( 10 frames prior to the onset of gape,
arbitrarily selected for each sequence). The timing differences between the
observed and calculated peak force were not significantly different than 0
(average 2.2±0.83 ms; RM-ANOVA F1,3=3.76,
P>0.15) and were linearly correlated (average
R2=0.78±0.06; average slope=0.89±0.09;
N=4 fish). Similarly, the peak calculated force was not significantly
different than the observed one (average deviation=–0.012±0.135
N; RM-ANOVA F1,3=0.45, P>0.54) and the two
magnitudes were correlated (average R2=0.59±0.07;
average slope=0.78±0.1; N=4 fish). Different symbols represent
data for the four fish studied, diagonal line represents the case of
X=Y.
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Fig. 6. Representative sequence of observed force (open circles), and the
calculated forces due to acceleration reaction (blue line), drag (green line)
and pressure gradient (red line). The three calculated forces sum to total
calculated force (black line). Note that pressure gradient force (an average
of 65.7% of total force) and acceleration reaction force (32.9%) peak
concurrently, while drag force (1.4%) peaks 0.7 ms later. The observed
and calculated forces are in good agreement throughout the strike
(R2=0.84, P<0.001).
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Fig. 7. The simulated change in calculated peak force (open circles) as a function
of strike initiation distance in a representative strike. Force was modeled
based on original strike kinematics, with strike initiation distance
systematically changed from 0.5–20 mm in 0.5 mm increments. Grey shaded
region is the 90% force efficiency zone, in which peak force for each
simulated strike was  90% of the maximal force within the simulated range.
The observed strike initiation distance for this sequence is also noted (9.6
mm; filled circle; marked `Obs'). The flow speed within the buccal cavity was
assumed equal to that at the mouth aperture, hence the flat response of peak
force at short strike-initiation distances.
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Fig. 8. Strike precision in bluegill. Observed strike starting distance is the
distance between the prey's eye and the center of the fish's mouth at the
moment of strike initiation (initiation of gape expansion). The distance of
maximal force was estimated by calculating the expected force achieved, with
the observed kinematics, for strike starting distances between 0.5 and 20 mm,
in 0.5 mm intervals. The distance of maximal force (defined as the distance
associated with the highest peak force) was not significantly different than
the observed strike initiation distance (average 1.9±3.6 mm; RM-ANOVA
F1,3=2.9, P>0.1). The distance associated with
the maximal peak force was linearly correlated with the observed distance
(average R2=0.49±0.25; average
slope=0.85±0.22; N=4 fish). Diagonal line represents the case
of X=Y.
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© The Company of Biologists Ltd 2007
