The effect of flow speed and body length on swimming kinematics of rainbow trout in a vortex street
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1
The Whitney Laboratory for Marine Bioscience, University of Florida, Biology, United States
The study of fish swimming in a vortex street has provided key insights into understanding how fish relate with vortices, but currently we have little understanding of how flow velocity or fish size affects this behavior. The present study tests the effect of wide range of flow speeds (2.5 to 11.0 L s-1, where L = total length) on the swimming kinematics of trout behind a 5 cm diameter cylinder to better understand how fish most effectively use vortices. I recorded rainbow trout with high speed video and measure the following variables: tail-beat frequency, body wavelength, maximum amplitude of four body locations (the tail tip, a point 50% down the body, the center of mass, and the tip of the snout), minimum amplitude and its location, maximum body curvature and its location, and maximum head angle. In addition, I tested the effect of body length on kinematics across speeds. I show that certain kinematic variables have a predictable pattern of change as flow speed increases, while others do not. Deviations of kinematic variables from the wake parameters were determined a priori using the 95% confidence intervals for each kinematic value at each flow speed. I found that tailbeat frequency is generally similar to the vortex shedding frequency of the cylinder at all but the lowest speed. Body wavelength and lateral body amplitudes increase with flow speed up to a point, after which values decrease. Trout have a longer body wavelength than the expected cylinder wake wavelength at intermediate speeds. Head angle is relatively constant at low to intermediate speeds and then increases dramatically at higher speeds. At the lowest speed, swimming kinematics behind a cylinder are identical to the kinematics of fish swimming in the freestream (i.e. no cylinder). At the highest speeds, swimming kinematics behind a cylinder reflect a close synchronization to the cylinder wake. Using a model I least square regression analysis, I found that only variables that increased significantly with flow speed were tailbeat frequency and body amplitudes (p < 0.01). Larger fish typically do not conform to the cylinder shedding frequency and wake wavelength as closely as smaller fish. While fish will position themselves in the cylinder wake at the highest speeds, this behavior cannot be sustained and fish are quickly drawn upstream and ejected from the vortex street. I hypothesize that trout cannot remain in the vortex street at fast flow speeds due to challenges in stability and control; the vortex street becomes much stronger and more turbulent in three-dimensions.
Acknowledgements
I would like to thank Masashige Taguchi and Christina Walker for assistance in data collection, analysis and fish care. Support was provided by NIH 1RO1DC010809-01 to J.C.L.
Keywords:
Biomechanics,
fish,
Karman gait,
kinematics,
Swimming,
Turbulence,
vortex street
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for Participant Symposium)
Topic:
Motor Systems
Citation:
Liao
JC
(2012). The effect of flow speed and body length on swimming kinematics of rainbow trout in a vortex street.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00164
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Received:
27 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Dr. James C Liao, The Whitney Laboratory for Marine Bioscience, University of Florida, Biology, St. Augustine, FL, 32080, United States, jliao@whitney.ufl.edu