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Fig. 1. (A) Schematic drawing of the experimental set-up, a goldfish and a vortex
ring. The pipette tip used to generate the vortex is at the left. The
elevation of the pipette (y-axis) was always at the height of the
fish's trunk lateral line canal. The rostro-caudal distance (x-axis)
between the pipette tip and the neuromast was adjusted to 5 cm. The lateral
distance (z-axis) of the pipette tip to the operculum of the fish was
0.5 cm, if not stated otherwise. A laser sheet was used to illuminate the
particles added to the water. In all cases in which we obtained PIV data and
neuronal data, the laser sheet illuminated the x–y
plane (yellow), i.e. a plane that was perpendicular to the fish's
rostro-caudal axis. The x–y plane was placed as close
to the skin as possible. For a further characterization of the water motions
caused by a vortex ring, the laser sheet was also positioned in the
z–x plane (red) or in the z–y
plane (gray). (B) Vectors (arrows) and vorticity (blue, counterclockwise; red,
clockwise) of the particle motions recorded 400 ms after valve opening
measured in the horizontal (z–x) plane (see A) in the
absence of a fish. (C,D) Velocities (v) directed parallel to the
x-axis, calculated from the vectors highlighted by the longitudinal
boxes in B. The plot in C transects the vortex through its midline and reveals
the central flow. The plot in D transects the laser sheet in the
z-axis. Here, the central flow is bordered by two vortex cores of
minimal velocity and a region where the flow direction is opposite to the jet
flow. The diameter of the vortex ring is approximately 3 cm.
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