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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
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
* Author for correspondence (e-mail: raholzman{at}ucdavis.edu)
Accepted 17 July 2007
During aquatic suction feeding, the predator opens its mouth and rapidly
expands its buccal cavity, generating a flow field external to the mouth. The
rapid expansion of the buccal cavity produces high fluid velocities and
accelerations that extend only a short distance from the mouth (about half of
one mouth diameter), and only persist for several milliseconds. Therefore, the
predator must precisely time its strike to locate the prey within the narrow
region of high flow, during the brief period when flow is at its peak. With
flow being the agent for transferring force to the prey, the predator may
enhance these forces by producing higher water velocities and faster
acceleration at the mouth, but also through increasing the strike's accuracy,
i.e. locating the prey closer to the mouth at the instant of peak flow speed.
The objectives of this study were to directly measure forces exerted by
bluegill Lepomis macrochirus on their prey and to determine how
bluegill modify force output. Bluegill were offered ghost shrimp tethered to a
load cell that recorded force at 5000 Hz, and feeding sequences were
synchronously recorded using 500 Hz video. Peak forces exerted on attached 20
mm shrimp ranged from 0.005 N to 0.506 N. In accordance with the short
duration of the strikes (average time to peak gape of 
13 ms), the forces
recorded were brief (12 ms from initiation to peak force), and force
magnitude declined rapidly after peak force. Statistical analysis indicated
that rate of buccal expansion, and prey size, but not strike initiation
distance, significantly affected peak force. These observed variables were
used with results from flow visualization studies to estimate the flow at the
prey's location, which allowed the calculation of drag, pressure gradient
force and acceleration reaction force. The relationship between these
calculated forces and the measured forces was strong, indicating that the
model can be used to estimate forces from strike kinematics. This model was
then used to study the effects of strike initiation distance on peak force and
on the rate of increasing force. Comparisons of model output to empirical
results indicated that bluegill time their strike so as to exert an average of
70% of the peak possible force on the prey, and that the observed strike
initiation distance corresponded to the distance that maximized modeled force
on an attached prey. Our results highlight the ability of bluegill to produce
high forces on their prey, and indicate that precision and visual acuity play
important roles in prey acquisition, beyond their recognized role in prey
detection.
Key words: Lepomis macrochirus, kinematics, prey capture, strike performance accuracy, suction feeding, force
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