| Median fin function in bluegill sunfish Lepomis macrochirus: streamwise vortex structure during steady swimming. | |
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MedLine Citation:
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PMID: 16574809 Owner: NLM Status: MEDLINE |
Abstract/OtherAbstract:
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Fishes have an enormous diversity of body shapes and fin morphologies. From a hydrodynamic standpoint, the functional significance of this diversity is poorly understood, largely because the three-dimensional flow around swimming fish is almost completely unknown. Fully three-dimensional volumetric flow measurements are not currently feasible, but measurements in multiple transverse planes along the body can illuminate many of the important flow features. In this study, I analyze flow in the transverse plane at a range of positions around bluegill sunfish Lepomis macrochirus, from the trailing edges of the dorsal and anal fins to the near wake. Simultaneous particle image velocimetry and kinematic measurements were performed during swimming at 1.2 body lengths s(-1) to describe the streamwise vortex structure, to quantify the contributions of each fin to the vortex wake, and to assess the importance of three-dimensional flow effects in swimming. Sunfish produce streamwise vortices from at least eight distinct places, including both the dorsal and ventral margins of the soft dorsal and anal fins, and the tips and central notched region of the caudal fin. I propose a three-dimensional structure of the vortex wake in which these vortices from the caudal notch are elongated by the dorso-ventral cupping motion of the tail, producing a structure like a hairpin vortex in the caudal fin vortex ring. Vortices from the dorsal and anal fin persist into the wake, probably linking up with the caudal fin vortices. These dorsal and anal fin vortices do not differ significantly in circulation from the two caudal fin tip vortices. Because the circulations are equal and the length of the trailing edge of the caudal fin is approximately equal to the combined trailing edge length of the dorsal and anal fins, I argue that the two anterior median fins produce a total force that is comparable to that of the caudal fin. To provide additional detail on how different positions contribute to total force along the posterior body, the change in vortex circulation as flow passes down the body is also analyzed. The posterior half of the caudal fin and the dorsal and anal fins add vortex circulation to the flow, but circulation appears to decrease around the peduncle and anterior caudal fin. Kinematic measurements indicate that the tail is angled correctly to enhance thrust through this interaction. Finally, the degree to which the caudal fin acts like a idealized two-dimensional plate is examined: approximately 25% of the flow near the tail is accelerated up and down, rather than laterally, producing wasted momentum, a loss not present in ideal two-dimensional theories. |
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Authors:
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Eric D Tytell |
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Publication Detail:
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Type: Journal Article; Research Support, U.S. Gov't, Non-P.H.S. |
Journal Detail:
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Title: The Journal of experimental biology Volume: 209 ISSN: 0022-0949 ISO Abbreviation: J. Exp. Biol. Publication Date: 2006 Apr |
Date Detail:
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Created Date: 2006-03-31 Completed Date: 2006-07-13 Revised Date: 2006-11-15 |
Medline Journal Info:
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Nlm Unique ID: 0243705 Medline TA: J Exp Biol Country: England |
Other Details:
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Languages: eng Pagination: 1516-34 Citation Subset: IM |
Affiliation:
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Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA. tytell@post.harvard.edu |
Export Citation:
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| MeSH Terms | |
Descriptor/Qualifier:
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Animal Structures
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anatomy & histology,
physiology Animals Biomechanics Perciformes / anatomy & histology*, physiology* Swimming / physiology* |
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine
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