Volumetric imaging of fish locomotion

Abstract

Fishes use multiple flexible fins in order to move and maintain stability in a complex fluid environment. We used a new approach, a volumetric velocimetry imaging system, to provide the first instantaneous three-dimensional views of wake structures as they are produced by freely swimming fishes. This new technology allowed us to demonstrate conclusively the linked ring vortex wake pattern that is produced by the symmetrical (homocercal) tail of fishes, and to visualize for the first time the three-dimensional vortex wake interaction between the dorsal and anal fins and the tail. We found that the dorsal and anal fin wakes were rapidly (within one tail beat) assimilated into the caudal fin vortex wake. These results show that volumetric imaging of biologically generated flow patterns can reveal new features of locomotor dynamics, and provides an avenue for future investigations of the diversity of fish swimming patterns and their hydrodynamic consequences.

Volumetric imaging of shark tail hydrodynamics reveals a three-dimensional dual-ring vortex wake structure

“…Just as the use of three-dimensional kinematics was imperative to determine the position of the shark tail during locomotion and for rejecting models of tail function based on two-dimensional views [16], it is now apparent that volumetric study of hydrodynamics is necessary for a complete, instantaneous view of wake structures [24]. The vertically oriented ring-within-a-ring vortex ring structure proposed by Wilga & Lauder [13] using two-dimensional methods was a sensible interpretation of the planar view PIV, but the single two-dimensional slice did not give enough information for a correct interpretation in three dimensions (figure 5).…”

“…Using an instantaneous volumetric PIV system [21,24,25], we were able to capture series of complete three-dimensional snapshots of the wake structure produced by the heterocercal tails of freely swimming sharks. Four live sharks (mean total length ¼ 24.6 cm), two each of two species, spiny dogfish (Squalus acanthias; see electronic supplementary material) and chain dogfish (Scyliorhinus retifer) with trailing edge spans of 5 -6.5 cm and tail beat amplitudes of 6.5-7.5 cm swam at 0.5, 0.75 and 1.0 body lengths per second in a recirculating flow tank equipped with a volumetric PIV system that captured volumes of 14 Â 14 Â 10 cm 3 (x, y, z) at 7.25 Hz (TSI Inc., Shoreview, MN, USA).…”

“…The volume of interest (14 Â 14 Â 10 cm) downstream of the swimming shark or robot was illuminated by a 120 mJ dual-head pulse laser [24]. The laser was pulsed at a frequency of 14.5 Hz, which was synchronized with recording capture by the volumetric 3-component velocimetry (V3V) volumetric flow imaging tripod camera probe (TSI Incorporated, Shoreview, MN, USA).…”

Speciation through the lens of biomechanics: locomotion, prey capture and reproductive isolation

“…With DPIV, water surrounding the fish is seeded with neutrally buoyant particles, a laser sheet illuminates those particles, and the movement of the particles can then be imaged with high-speed video. The two-dimensional and three-dimensional global flow fields can be calculated from spatial cross-correlation techniques to help reveal the fluid basis of fish function and behaviour [84]. For example, threedimensional suction accuracy in centrarchid fishes was recently modelled and related to capture success [85].…”

Measurement of hydrodynamic force generation by swimming dolphins using bubble DPIV

“…Laboratory experiments using DPIV were conducted using laser sheets to illuminate ~10 μm diameter silvercoated glass beads in the wake of the fish (Fish and Lauder, 2006;Flammang et al, 2011). Based on the movement of the glass beads, velocity data were used to quantify the thrust-producing momentum jet and vortices.…”