Affiliation:
1. Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697, USA and
2. Museum of Comparative Zoology, Harvard University, 26 Oxford Street, Cambridge, MA 02138, USA
Abstract
SUMMARYA key evolutionary transformation of the locomotor system of ray-finned fishes is the morphological elaboration of the dorsal fin. Within Teleostei, the dorsal fin primitively is a single midline structure supported by soft, flexible fin rays. In its derived condition, the fin is made up of two anatomically distinct portions: an anterior section supported by spines, and a posterior section that is soft-rayed. We have a very limited understanding of the functional significance of this evolutionary variation in dorsal fin design. To initiate empirical hydrodynamic study of dorsal fin function in teleost fishes, we analyzed the wake created by the soft dorsal fin of bluegill sunfish (Lepomis macrochirus) during both steady swimming and unsteady turning maneuvers. Digital particle image velocimetry was used to visualize wake structures and to calculate in vivo locomotor forces. Study of the vortices generated simultaneously by the soft dorsal and caudal fins during locomotion allowed experimental characterization of median-fin wake interactions.During high-speed swimming (i.e. above the gait transition from pectoral- to median-fin locomotion), the soft dorsal fin undergoes regular oscillatory motion which, in comparison with analogous movement by the tail, is phase-advanced (by 30% of the cycle period) and of lower sweep amplitude (by 1.0cm). Undulations of the soft dorsal fin during steady swimming at 1.1bodylengths−1 generate a reverse von Kármán vortex street wake that contributes 12% of total thrust. During low-speed turns, the soft dorsal fin produces discrete pairs of counterrotating vortices with a central region of high-velocity jet flow. This vortex wake, generated in the latter stage of the turn and posterior to the center of mass of the body, counteracts torque generated earlier in the turn by the anteriorly positioned pectoral fins and thereby corrects the heading of the fish as it begins to translate forward away from the turning stimulus. One-third of the laterally directed fluid force measured during turning is developed by the soft dorsal fin. For steady swimming, we present empirical evidence that vortex structures generated by the soft dorsal fin upstream can constructively interact with those produced by the caudal fin downstream. Reinforcement of circulation around the tail through interception of the dorsal fin’s vortices is proposed as a mechanism for augmenting wake energy and enhancing thrust.Swimming in fishes involves the partitioning of locomotor force among several independent fin systems. Coordinated use of the pectoral fins, caudal fin and soft dorsal fin to increase wake momentum, as documented for L. macrochirus, highlights the ability of teleost fishes to employ multiple propulsors simultaneously for controlling complex swimming behaviors.
Publisher
The Company of Biologists
Subject
Insect Science,Molecular Biology,Animal Science and Zoology,Aquatic Science,Physiology,Ecology, Evolution, Behavior and Systematics
Reference64 articles.
1. Aleev, Y. G. (1969). Function and Gross Morphology in Fish (translated from the Russian by M. Raveh). Jerusalem: Keter Press.
2. Alexander, R. McN. (1974). Functional Design in Fishes, third edition. London: Hutchinson & Co.
3. Anderson, J. (1996). Vorticity control for efficient propulsion. PhD thesis, MIT/WHOI, 96-02.
4. Anderson, J. M., Streitlien, K., Barrett, D. S. and Triantafyllou, M. S. (1998). Oscillating foils of high propulsive efficiency. J. Fluid Mech.360, 41–72.
5. Arita, G. S. (1971). A re-examination of the functional morphology of the soft-rays in teleosts. Copeia1971, 691–697.
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