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First published online March 22, 2004
Journal of Experimental Biology 207, 1585-1596 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.00922

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The hydrodynamic trails of Lepomis gibbosus (Centrarchidae), Colomesus psittacus (Tetraodontidae) and Thysochromis ansorgii (Cichlidae) investigated with scanning particle image velocimetry

Wolf Hanke^* and Horst Bleckmann

Institut für Zoologie der Rheinischen Friedrich-Wilhelms-Universität Bonn, Poppelsdorfer Schloß, D-53115 Bonn, Germany

View larger version (30K): [in a new window]   Fig. 1. Experimental set-up in (A) top view and (B) front view. Fish were trained to swim on a straight line through the middle of the experimental tank to reach a goal compartment where they received a food reward. Before a trial, an individual fish was kept in a starting compartment for at least 5 min. Six horizontal light sheets (thin illuminated layers of laser light) were installed in the middle of the tank. The water was seeded with neutrally buoyant particles. Cameras 1 and 2 recorded the movements of the seeding particles from above the tank. Cameras 3 and 4 recorded the fish's movements.

View larger version (35K): [in a new window]   Fig. 2. Silhouette of Lepomis gibbosus as it swam through the field of view. For clarity, the silhouettes were shifted laterally; the curved line connecting circles in the centre of the figure indicates the position of the fish`s head in successive images.

View larger version (258K): [in a new window]   Fig. 3. (A,B) Fish wake of Lepomiss gibbosus in six layers as velocity vector fields. The different layers are indicated by the laser number in the upper left corner of each vector plot, where laser 1 illuminated the uppermost and laser 6 the lowermost layer. The illuminated layers were spaced equidistantly (12 mm apart). Water velocities and divergence are shown at t10 s (A) and t60 s (B) (t=0 s is the time when the fish entered the field of view; times of vector fields are slightly different because of the scanning procedure). Divergence is defined as (d/dx) vx + (d/dy) vy (x and y are the cartesian coordinates, vx and vy are the x and y components of the velocity) and indicates the flow out of or into a small section of the plane, which is caused by out-of-plane movements.

View larger version (49K): [in a new window]   Fig. 4. (A–C) Velocity and vorticity values for one trial with Lepomis (A), one trial with Colomesus (B) and one with Thysochromis (C) as function of time (60 s). Maximum velocity in the field of view (top), mean velocity in the field of view (middle) and maximum vorticity in the field of view (bottom) are shown. Different colours refer to different layers (black, layer 1 = uppermost layer; red, layer 2; green, layer 3; blue, layer 4; cyan, layer 5; magenta, layer 6 = lowermost layer.

View larger version (94K): [in a new window]   Fig. 5. Visualisation of the spatial extent of the fish's wakes. For this figure, each vector field was reduced to a row by averaging over the columns of the vector field, and the rows resulting from this procedure were assembled in temporal order. Note that the velocity scale does not cover the complete range of measured values (cf. Figs 3, 4 and Table 1) in order to resolve the low velocities in the aged trail. A shows two Lepomis wakes, B shows two Colomesus wakes and C shows two Thysochromis wakes (see Table 1 for survey of trials).

View larger version (10K): [in a new window]   Fig. 6. The trails from tank 2 related to their trail indices TI1 and TI2 (see text and Table 3). Lepomis, triangles; Colomesus, crosses; Thysochromis, squares.