Fig. 1. (A) Fins and axes of instability in bluegill sunfish. Paired fins in bluegill are represented by the pectoral (Pcf) and pelvic fins (Plf). Dorsal (Df), anal (Af) and caudal (Cf) fins are median fins. Fins work to control the forces that act on the fish in three major axes; pitch (head up and down movement), roll (body rotating along its longitudinal axis) and yaw (head side to side movement). (B) Schematic cross-section showing centre of mass (COM), centre of buoyancy (COB) and fin placement. The white oval in the centre of the fish represents the swim bladder cavity of the animal. The area of the fin surface as well as its location relative to the fish's centre of mass and centre of buoyancy will determine the amount of torque a fin can impose on the body at a given velocity. Distance of the dorsal fin (Distance_d) and anal fin (Distance_a) are marked from the midpoint between the COM and COB. F_d, dorsal fin force; F_a, anal fin force.