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First published online August 17, 2007
Journal of Experimental Biology 210, 2979-2989 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.006437

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Swimming in the upside down catfish Synodontis nigriventris: it matters which way is up

Robert W. Blake^* and Keith H. S. Chan

Department of Zoology, University of British Columbia, Vancouver, British Columbia, V6T 1Z4, Canada

View larger version (26K): [in this window] [in a new window]   Fig. 1. Drag versus water depth for S. nigriventris (inset) for dorsal side up (A) and inverted posture (B) for water velocities of 0.38 m s–1 (open squares), 0.47 m s–1 (open diamonds), 0.55 m s–1 (open triangles) and 0.63 m s–1 (crosses). Values are means ± 2 s.e.m. For N values, see text. In all cases, r2>0.9, P<0.05.

View larger version (5K): [in this window] [in a new window]   Fig. 2. Drag augmentation factor () versus submersion depth index (h/d, where h is the distance from the water surface to the center line of the fish and d is maximum body depth) in the dorsal side up (A) and inverted (B) posture.

View larger version (9K): [in this window] [in a new window]   Fig. 3. Total near-surface drag (sum of wave, pressure and friction drags) measurements for body orientation angles of 0°, 20°, 45° and 90° for dorsal side up (A) and inverted (B) posture for water velocities of 0.38 m s–1 (open squares), 0.47 m s–1 (open diamonds), 0.55 m s–1 (open triangles) and 0.63 m s–1 (crosses). Values are means ± 2 s.e.m. For N values, see text. In all cases, r2>0.9, P<0.05.

View larger version (8K): [in this window] [in a new window]   Fig. 4. Centrelines (tip of the snout and centre of mass indicated by arrowheads and filled red circles, respectively) for S. nigriventris during a steady swimming bout (A) and fast-start (B) in the inverted posture at intervals of 0.032 s and 0.004 s, respectively, indicated by successive numbers.

View larger version (27K): [in this window] [in a new window]   Fig. 5. Tailbeat frequency, amplitude and stride length versus water velocity during steady swimming bouts for S. nigriventris: dorsal side up near the surface (0.025 m, h/d=0.6, green open circles; 0.04 m, h/d=1.2, red open circles) and deeply submerged (0.09 m, h/d=3.4, blue open circles); inverted near the surface (0.025 m, h/d=0.6, green open squares; 0.04 m, h/d=1.2, red open squares) and deeply submerged (0.09 m, h/d=3.4, blue open squares). Regressions for tailbeat frequency and stride length are represented by solid (dorsal side up) and dotted lines (inverted posture). Since ANCOVA shows no significant effects of water depth on amplitude (P>0.05), the data were pooled to generate an overall regression (black solid line). In all cases, r2>0.4, P<0.05.

View larger version (5K): [in this window] [in a new window]   Fig. 6. Proportion of fast-start mechanical energy lost versus submersion depth index (h/d) for S. nigriventris, dorsal side up (blue) and inverted posture (red), and rainbow trout (black) (Webb et al., 1991) after 20 ms (open circles), 40 ms (filled circles), 60 ms (filled triangles), 80 ms (open squares) and 100 ms (filled squares).