Fig. 12. Proposed 3D vortex structure around a swimming bluegill sunfish. Vortex loops are shed off the caudal, dorsal and anal fins, shown in green, red and blue, respectively. Vortex filaments and their directions are shown by solid arrowheads. The direction of vortex rotation, derived by the right hand rule from the filament direction, is shown with open arrowheads where there is space. (A) 3D view, showing the proposed linkages between caudal fin tip vortices and dorsal and anal fin vortices. Question marks are shown where the connection between dorsal or anal fin vortices and the caudal fin wake is unclear. The notch vortices in the far wake are shown by dotted lines, indicating that the structure is hydrodynamically unstable and may not persist in the form shown. A projection of the vortex structure in the horizontal plane is shown below, with dotted lines indicating the correspondence between the projection and four centers of rotation. Note that the projection is taken from multiple horizontal planes. A midline tracing, in the correct phase, is shown below the fish. (B) Side views of the vortex filaments shown in A as the fish swims from left to right, showing how the dorsal and anal fin vortex filaments could potentially join up to the caudal fin vortices. Notch vortices in the far wake are again shown dotted to indicate their instability. (C) Schematic of the progression of the outer dorsal fin vortex and its interaction with the caudal fin, shown at three points in time from top to bottom. The fish is holding station in flow moving from right to left. L, low pressure zones that would be formed along the tail due to the proximity of the outer dorsal fin vortex.