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Steady swimming muscle dynamics in the leopard shark Triakis semifasciata

Jeanine M. Donley^* and Robert E. Shadwick

Marine Biology Research Division, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0202, USA

View larger version (44K): [in a new window]   Fig. 1. (A) Leopard shark image modified from Miller and Lea (1972). The red bar represents the longitudinal range of red muscle and the arrows indicate the three axial positions examined in this study. (B) Post-mortem dissection showing the lateral band of red muscle at 0.42 L and placement of a sonometric crystal (indicated by the arrow).

View larger version (41K): [in a new window]   Fig. 2. (A) An example of electromyographic (EMG) and sonometric traces recorded simultaneously over several consecutive tailbeat cycles at three axial positions in an 88.0 cm leopard shark. (B) Close-up of one tailbeat cycle. Vertical lines indicate onset and offset of EMG activity.

View larger version (115K): [in a new window]   Fig. 3. Dorsal view (A) and lateral view (B) of a 94.5 cm leopard shark swimming in the swim tunnel. Dorsal images were obtained during steady swimming concurrent with sonometric and EMG recordings in order to correlate midline kinematics with measurements of red muscle strain and activation.

View larger version (14K): [in a new window]   Fig. 4. An example of red muscle strain measured over six consecutive tailbeat cycles in the anterior (blue), mid (black), and posterior (green) positions in a 77.0 cm leopard shark. Strain amplitudes varied significantly between the three body positions (P<0.050) in all sharks examined.

View larger version (16K): [in a new window]   Fig. 5. Timing of muscle activation at three axial positions. Offset of activation (A) occurred during muscle shortening and onset (B) occurred during muscle lengthening at all positions in all leopard sharks examined. There was no significant longitudinal variation in the phase of activation in all individuals examined. Values are means ± S.D. calculated for several tailbeat cycles in each fish.

View larger version (13K): [in a new window]   Fig. 6. Maximum lateral displacement (% L) of the dorsal midline as a function of body position. Values represent mean ± S.E.M. of maximum displacement for nine leopard sharks swimming at 1.0 L s–1. Lateral displacement was greatest at the tip of the caudal fin.

View larger version (39K): [in a new window]   Fig. 7. Red muscle strain (solid line) measured by sonomicrometry superimposed onto predicted strain (open circles) calculated from midline curvature for five tailbeat cycles at three body positions, anterior (A), mid (B) and posterior (C), in a 94.5 cm leopard shark, to illustrate the similarity between values of predicted and measured strain. The phase of measured strain closely matched the phase of local midline curvature (open circles, right axis), and thus predicted strain at all body positions in all individuals examined.

View larger version (20K): [in a new window]   Fig. 8. (A) Relative body thickness (mean ± S.E.M.) of five leopard sharks as a function of axial position. To compare individuals of different sizes, body thickness is normalized to thickness measured at 0.3 L. Thickness measurements were made from dorsal video images. (B) Dorsal midline curvature calculated for six positions along the body in eight leopard sharks swimming 1.0 L s–1. Values are means ± S.D. calculated from four tailbeat cycles for each fish at each body position.

View larger version (23K): [in a new window]   Fig. 9. EMG and sonometric data for three tailbeat cycles in an 88.0 cm leopard shark at three axial positions: anterior (A), mid (B) and posterior (C). The vertical lines indicate the phase of activation in the anterior axial position (0.42 L) and allow for comparison with the EMG/strain phases in the mid and posterior regions of the body.

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