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First published online December 28, 2007
Journal of Experimental Biology 211, 187-195 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.008128

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Escaping Flatland: three-dimensional kinematics and hydrodynamics of median fins in fishes

Eric D. Tytell^1,*, Emily M. Standen² and George V. Lauder²

¹ Department of Biology, University of Maryland, College Park, MD 20742, USA
² Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA

View larger version (9K): [in this window] [in a new window]   Fig. 1. Comparison of three-dimensional (3D) body shape and midline kinematics for a bass (Micropterus salmoides) and an eel (Anguilla rostrata). (A,C) Line drawings of the lateral profiles. (B,D) Midline tracings at equally spaced intervals of time during slow swimming at 0.7 lengths s–1 (L s–1) for the bass (modified from Jayne and Lauder, 1995) and 0.5 L s–1 for the eel (E.D.T., unpublished data). Scale bar is valid for both panels.

View larger version (34K): [in this window] [in a new window]   Fig. 2. Tips of the caudal, dorsal and anal fins in bluegill sunfish cup actively into the flow. The motion of fins through half a tail beat from left to right in two transverse planes is presented. Each panel shows seven tracings of the posterior margins of the fins, spaced equally in time, as seen from behind the fish. The color and thickness of the bar indicate the lateral velocity of a particular segment of the fin. The beat frequency for each fin is the same, 2.4 Hz. (A) Caudal fin kinematics. (B) Dorsal and anal fin kinematics. Inset in A shows position of the two planes. Scales are the same for A and B (from Tytell, 2006).

View larger version (13K): [in this window] [in a new window]   Fig. 3. Fin area in bluegill sunfish changes at different swimming speeds due to the elevation or depression of the fin rays. Bars show mean fin surface area at the time of maximum excursion and error bars represent s.e.m. Fin area at swimming speeds denoted with letter a differ significantly from those denoted by letter b (from Standen and Lauder, 2005).

View larger version (100K): [in this window] [in a new window]   Fig. 4. Posterior, dorsal and ventral views of maneuvering behaviors in bluegill sunfish. (A) Posterior view during a braking maneuver. Note the asymmetry of the caudal fin. The caudal edge of the dorsal fin is curled forward into the flow. Image courtesy of Brooke Flammang (unpublished data). (B,C) Dorsal and ventral views of a right turning maneuver. Both dorsal and anal fins show displacement of their trailing edges during this maneuver. Curvature of the fin surfaces is large, but the actual bending of each individual fin ray is small. Scale bars throughout are 1 cm (from Standen and Lauder, 2005).

View larger version (115K): [in this window] [in a new window]   Fig. 5. Representative flow fields near the dorsal and anal fins during steady swimming. Yellow arrows indicate flow velocity; colored contours show vorticity. Schematic diagrams above the plots indicate the approximate position and orientation of the light sheets. (A) Flow in a transverse plane near the posterior edges of the dorsal and anal fins of bluegill sunfish swimming at 1.2 L s–1. Vortices are shed along each dorsal and ventral edge of both the dorsal and anal fins. The caudal fin obscures some of the view (from Tytell, 2006). (B,C) Flow in horizontal planes at the level of the dorsal fin (B) and the anal fin (C) of trout swimming at 0.5 L s–1. The pelvic fins are visible on the left side of both images, and C shows both the anal fin (center) and some of the of the caudal fin (right) (from Standen and Lauder, 2007). Scale bars throughout are 5 mm and scale vectors are 5 cm s–1.

View larger version (157K): [in this window] [in a new window]   Fig. 6. Hydrodynamic function of the dorsal fin in yellow perch (Perca flavescens, 18.0 cm total length, L) to illustrate fin positions (left panels) and wake flows (right panels) during steady swimming at 0.5 L s–1. The spiny and soft dorsal fins and the dorsal lobe of the caudal fin have been illuminated with a horizontal laser light sheet for particle image velocimetry. (A) Fin positions and wake flows at a time when the soft dorsal fin has reached maximum excursion to the right; (B) Fin positions 292 ms later when the soft dorsal fin is at its maximal excursion to the left side of the perch. Note the shear layer resulting from the spiny and soft dorsal fins, evident as the elongated regions of red and blue vorticity in the right-hand panels. The soft dorsal fin also sheds a drag wake with regions of vorticity visible in the gap between the soft dorsal fin and the caudal fin. Images on the left have been contrast-enhanced to better reveal the laser-illuminated particles. Shadows where vectors were not calculated represent regions where the laser light sheet was blocked by the fish body or fins.

View larger version (143K): [in this window] [in a new window]   Fig. 7. Hydrodynamic function of the dorsal fin in yellow perch (Perca flavescens, 18.0 cm total length, L) to illustrate wake flows during a low-speed yawing turn elicited during steady swimming at 0.5 L s–1. A horizontal laser light sheet is illuminating both the spiny and soft portions of the dorsal fin, as well as the dorsal lobe of the caudal fin. Fin positions and wake flows are illustrated for the early, middle and late stages of the turn. The yellow arrows in the left-hand panels show the direction of fin surface motion from one panel to the next. Initial wake flows during the turn are generated by the soft dorsal fin (A). As the turn develops, both the soft dorsal and the caudal fin have generated distinct momentum jets, which result in a yawing turn of the perch body (B). At the end of the turn, each of the three fins has shed a distinct vortex ring (C). Images on the left have been contrast-enhanced to better reveal the laser-illuminated particles.

View larger version (24K): [in this window] [in a new window]   Fig. 8. Vortex filament model showing vortices near steadily swimming bluegill sunfish and brook trout. Numbers indicate vortex circulation (in mm2 s–1), to evaluate the relative vortex strengths, and the superscript letter identifies the source (see below). (A) 3D vortex structure for bluegill sunfish swimming at about 1.2 L s–1. Gaps in the dorsal and anal fin vortices in the wake indicate regions where the vortices should link up to the caudal fin vortices, but for which there are too few data to identify the topology of the filament. (B) Experimentally observed vortices for the dorsal, anal and caudal fins of trout swimming at 0.5 L s–1. Dotted lines in the caudal fin vortices indicate a region that might have a deformation, like in bluegill sunfish, but for which there are not appropriate data for any definitive conclusions. Sources of circulation data: a(Tytell, 2006); b(Drucker and Lauder, 2001) (estimated from published figures); c(Standen and Lauder, 2007); d(E.M.S. and G.V.L., unpublished data).

View larger version (46K): [in this window] [in a new window]   Fig. 9. Locomotion in yellow perch (Perca flavescens, 16.5 cm total length, L) to illustrate the function of the dorsal fin during steady swimming and a c-start escape response. Yellow perch have a dorsal fin with distinct spiny and `soft' portions, in contrast to bluegill sunfish (e.g. Fig. 8). (A,B) Frames from a high-speed video (250 Hz) of steady swimming at two speeds (0.5 and 1.0 L s–1). Note that the height of the anterior spiny and posterior soft portions of the dorsal fin as well as the anal fin decrease with increasing swimming speed (yellow arrows). (C) Dorsal fin conformation just prior to a c-start; (D) fin position toward the end of stage 1 of the c-start. The spiny portion of the dorsal fin is erected during stage 1 (yellow arrow), but the soft dorsal and anal fin show little change in area.

View larger version (97K): [in this window] [in a new window]   Fig. 10. Trout yawing maneuver at 0.5 L s–1. The fish is maneuvering away from the top of each image. The dorsal view is taken while the dorsal fin pauses at maximum excursion, showing a large shear layer along the left side of the fin and the formation of a strong lateral jet. The ventral view is taken just after the anal fin begins to return from maximum excursion; again a large shear layer is seen on the left side of the fin also accompanied by a large lateral jet. During yawing maneuvers, contralateral jet formation is typically weak, causing an imbalance in force production and moving the fish's body laterally away from the strong jet side of the fish. Shadows where vectors were not calculated represent regions where the laser light sheet was blocked by the fish body or fins (after Standen and Lauder, 2007).