Fig. 9. Locomotion in yellow perch (Perca flavescens, 16.5 cm total length, L) to illustrate the function of the dorsal fin during steady swimming and a c-start escape response. Yellow perch have a dorsal fin with distinct spiny and `soft' portions, in contrast to bluegill sunfish (e.g. Fig. 8). (A,B) Frames from a high-speed video (250 Hz) of steady swimming at two speeds (0.5 and 1.0 L s^–1). Note that the height of the anterior spiny and posterior soft portions of the dorsal fin as well as the anal fin decrease with increasing swimming speed (yellow arrows). (C) Dorsal fin conformation just prior to a c-start; (D) fin position toward the end of stage 1 of the c-start. The spiny portion of the dorsal fin is erected during stage 1 (yellow arrow), but the soft dorsal and anal fin show little change in area.