Fig. 7. Regions around a cylinder in flow that trout will either entrain (defined as two rectangular regions on either side of the cylinder, 7x15 cm) or Kármán gait (defined as a single rectangle centered along the midline of the cylinder wake, 10x15 cm). In the light, fish prefer to Kármán gait in the vortex street downstream from the cylinder (black fill) for the majority of the time during a 60-min experiment, especially when the lateral line is intact (V+L+₁). Values for fish in the light with an intact lateral line exposed to the cylinder for two consecutive days (V+L+₂) are almost identical to those exposed for 1 day (V+L+₁), indicating that previous experience in the flow tank does not alter the preference to Kármán gait. In contrast to their reaction in the light, fish in the dark do not spend much time in the vortex street regardless of lateral line functionality (V–L+₁ or V–L–₂), preferring to entrain (gray fill) just downstream and to the side of the cylinder. The time that fish spent exploring other regions of the flow tank (white) is similar across treatments.