Fig. 1. Filming arrangement. (A) Flow tank filming configuration seen from above. Two cameras film the fish from behind through a front-surface mirror at 45° in the flow downstream of the fish. The mirror, fish, and camera positions are approximately to scale relative to the flow tank width. A laser light sheet is projected in from the side. One camera views the sheet orthogonally; the other is at a 12° angle. The off-axis camera uses a Scheimpflüg lens mount to tilt the axis of the lens and focus on the entire light sheet, despite the camera's angle. The x axis is lateral, from the fish's left to right, and the z axis is streamwise in the flow direction. (B) Side view of the filming configuration, showing the ventral view camera used for kinematic measurements. PIV cameras are omitted. The y axis is dorso-ventral and the z axis is streamwise. (C) Sample image from the orthogonal PIV view. (D) Sample image from the ventral view. (E) Terminology for regions in which streamwise vortices are shed. Sources of vortices along the body are indicated by thick colored lines.