First published online July 6, 2005
Journal of Experimental Biology 208, 2653-2660 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01682
Sucking while swimming: evaluating the effects of ram speed on suction generation in bluegill sunfish Lepomis macrochirus using digital particle image velocimetry
Timothy E. Higham*,
Steven W. Day and
Peter C. Wainwright
Section of Evolution and Ecology, University of California, One
Shields Avenue, Davis, CA 95616, USA
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Fig. 1. The experimental setup used in this study. In order to elicit varying ram
speeds at the time of capture the prey was introduced at one of three
distances from the sunfish: 0 cm (A), 30 cm (B), and 50 cm (C). Note that
mirrors were positioned below and above the tank to reflect the laser sheet up
and then down in order to illuminate both above and below the head of the fish
during feeding.
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Fig. 2. Representative images, with streamlines and contours of fluid speed in the
fish's frame of reference at the time of maximum gape for a low ram case (A;
RS/AFSaperture=0%), a medium ram case (B;
RS/AFSaperture=6%), and a high ram case (C;
RS/AFSaperture=14%). Note that the streamlines do
not indicate the area of water ingested, but rather the instantaneous
direction of movement of water at each location in space.
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Fig. 3. Sample images illustrating a large height-to-length ratio of the ingested
volume (A) and a trial with a small height/length ratio (B). Both images are
taken at the time of 20% of peak gape and the white outlines indicate the
volume of water that was captured during the feeding event. The fish in (A)
was moving at 0 cm s–1 and the fish in (B) was moving at 17.5
cm s–1 at the time of peak gape.
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Fig. 4. Representative sequences from a high ram case (A;
RS/AFSaperture=19%) and a low ram case (B;
RS/AFSaperture=3%) showing the similarity in
timing of events. Note that maximum suction speed coincided with peak gape or
slightly preceded it. RS, ram speed; AFS, fluid speed.
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Fig. 5. (A) Time to peak gape (TTPG) vs AFS1/2 PG for
all trials separated into ram speeds below and above 10 cm
s–1. (B) Residuals from the regression of maximum suction
speed and TTPG vs ram speed. There was a significant effect of
TTPG, but not ram speed, on maximum flow speed.
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Fig. 6. Ram speed vs degree of focusing (DF) of water entering the mouth
(log–log plot). Note that values of DF for ram speeds equal to 0 cm
s–1 are not shown because they are equal to infinity.
r2=0.81, P<0.05.
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Fig. 7. The relationship between ram speed and the shape of the ingested volume of
water. Only feedings using worm as prey are shown. Points with lower values of
height/length ratio have a more elongated, narrow shape of ingested water.
r2=0.44, P<0.05.
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Fig. 8. The relationship between fluid speed AFS and distance from the
mouth aperture (scaled to maximum mouth diameter) and the predicted effects of
ram speed RS (RS/AFSaperture=20% in this
case) on this relationship. The blue line represents AFS for a
stationary fish and the red line AFS for a fish with a RS of
20 cm s–1. Note that RS has a much greater effect on
AFSaperture than AFS1/2 PG. The length
of the green arrow represents the magnitude of body closing speed of a
stationary fish (25 cm s–1) and the length of the black arrow
represents the magnitude of body closing speed of a fish with a RS of
20 cm s–1 (40 cm s–1). Note that overall
body closing speed is increased with moderate levels of RS. The
relationship between fluid speed and distance from the mouth is from Day et
al. (2005 ).
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© The Company of Biologists Ltd 2005
