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First published online July 6, 2005
Journal of Experimental Biology 208, 2753-2763 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01706

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Dorsal and anal fin function in bluegill sunfish Lepomis macrochirus: three-dimensional kinematics during propulsion and maneuvering

E. M. Standen^* and G. V. Lauder

Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA

View larger version (18K): [in a new window]   Fig. 1. (A) Fins and axes of instability in bluegill sunfish. Paired fins in bluegill are represented by the pectoral (Pcf) and pelvic fins (Plf). Dorsal (Df), anal (Af) and caudal (Cf) fins are median fins. Fins work to control the forces that act on the fish in three major axes; pitch (head up and down movement), roll (body rotating along its longitudinal axis) and yaw (head side to side movement). (B) Schematic cross-section showing centre of mass (COM), centre of buoyancy (COB) and fin placement. The white oval in the centre of the fish represents the swim bladder cavity of the animal. The area of the fin surface as well as its location relative to the fish's centre of mass and centre of buoyancy will determine the amount of torque a fin can impose on the body at a given velocity. Distance of the dorsal fin (Distanced) and anal fin (Distancea) are marked from the midpoint between the COM and COB. Fd, dorsal fin force; Fa, anal fin force.

View larger version (52K): [in a new window]   Fig. 2. Experimental apparatus. (A) Fish swam in a multi-speed flow tank. Three high-speed digital cameras captured synchronous dorsal, ventral and lateral views of swimming fish. (B) Fin ray digitizing. Four points along every other fin ray, represented here as yellow (x) symbols and lines, were digitized in three dimensions using two simultaneous views (only the lateral view is shown here) to calculate fin area and fin ray curvature. Yellow dots represent the trailing edge of each fin as well as the body point that were digitized to calculate excursion and phase lag.

View larger version (18K): [in a new window]   Fig. 3. (A–F) Plots of fin excursion over time; typical of steady swimming (A-E) and maneuvering (F) in bluegill. All graphs portray the same fish swimming at the five steady swimming speeds and during a maneuver. The black line represents the excursion of the body, the solid red line represents the dorsal fin, and the broken blue line represents the anal fin.

View larger version (18K): [in a new window]   Fig. 4. Mean maximum excursion vs swimming speed. Maximum excursion increases with swimming speed. During steady swimming the dorsal fin (red) has larger excursions than the anal fin (blue) and both fins have greater excursions than the body (black). Unsteady maneuvers have highest maximum excursions and variation. Values are means ± 1 S.E.M. of all fish (N=4).

View larger version (80K): [in a new window]   Fig. 5. Dorsal, lateral and ventral views of a yawing maneuver to the right at the point of maximum fin excursion. Both dorsal and anal fins show displacement of their trailing edges during this maneuver. Curvature of fin surfaces is large, but the actual bending of each individual fin ray is small. Note that both dorsal and anal fins move to the same side of the fish. Bars, 1 cm.

View larger version (24K): [in a new window]   Fig. 6. Mean fin surface area at the time of maximum excursion. Fin area at swimming speeds denoted with letter A differ significantly from those denoted by letter B.

View larger version (23K): [in a new window]   Fig. 7. Maximum curvature vs swimming speed. Maximum curvatures denoted with letter A differ significantly from those denoted by letter B.

View larger version (21K): [in a new window]   Fig. 8. Average maximum curvature of individual fin rays. Average maximum curvature was calculated as the average of the three maximum curvature values for each ray. Data are taken from a single fish. Individual rays are plotted on the x-axis with ray 1 being the most anterior along the fin; rays 2–7 are located posteriorly in order. Each graph represents a single swimming speed or maneuver at the point of maximum excursion. Seven rays were analyzed from the dorsal fin (A) and nine rays from the anal fin (B).