Tutorial on Embodiment

3.2.1.1. Euthanized trout

 

Liao et al. conducted experiments with alive and euthanized trouts in water with and without vortices. These experiments show that fish exploit the physical characteristics of their environment by means of their body morphology to reduce energy consumption while swimming.

"Trout adopt a novel mode of locomotion to slalom in between experimentally generated vortices by activating only their anterior axial muscles. Reduced muscle activity during vortex exploitation compared with the activity of fishes engaged in undulatory swimming suggests a decrease in the cost of locomotion and provides a mechanism to understand the patterns of fish distributions in schools and riverine environments.

Periodic vortices of similar strength and size to each other were generated by using a vertically mounted D-section cylinder placed in water flowing at a known velocity. Vortices generated by the D-section cylinder were similar in strength to those produced by other freely swimming fish.

Compared with swimming in free stream (uniform) flow, there are two hydrodynamic benefits of station holding behind a cylinder. Fish can simply swim against the current in the region of reduced flow, drafting, for example, as a bicyclist would behind another bicyclist, or they can generate lift to move against the flow by altering their body kinematics to synchronize with the shed vortices. Because energy can be captured from cylinder vortices, trout that synchronize their body kinematics to vortices appropriately may need to use very little energy and, thus, gain a hydrodynamic advantage beyond that of drafting in the reduced velocity alone." (Liao et al. 2003)

 

Video 3.2.1.1.1. Alive trout swimming in free stream flow. Increased muscle activity is measured here. (courtesy Dr. Liao)


 

Video 3.2.1.1.2 Alive trout holding station behind a cylinder. Reduced muscle activity is measured compared to swimming in free stream flow. (courtesy Dr. Liao)


Video 3.2.1.1.3 "Euthanized trout towed behind a cylinder. A line marking the region of the suction zone, defined as two diameters downstream of the cylinder, is drawn for reference. At times, the intrinsic compliance of the musculoskeletal system causes the body to synchronize with the shedding cylinder vortices such that the body produces thrust passively and moves upstream. Once inside the suction region, the body is drawn forward until the head hits the cylinder." (courtesy Dr. Liao, Whitney Lab website)


References:

Liao, J. Beal, D. N. Lauder, G. V. and Triantafyllou, M. S. (2003). Fish exploiting vortices
decrease muscle activity. Science 302, 1566-1569.
Taguchi, M., Liao, J. (2011). Rainbow trout consume less oxygen in turbulence: the energetics of swimming behaviors at different speeds. The Journal of Experimental Biology 214, 1428-1436.

 

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