Fig. 9. Summary of stroke-averaged locomotor forces generated by three fin systems in sunfish. Each force is reported as mean ± S.E.M. (N=6–11 fin beats) with the corresponding percentage of total force generated by all fins given in parentheses. (A) Thrust produced during steady swimming at 1.1Ls^-1, where L is total body length. Dorsal and caudal fin forces are calculated from the momentum of three frontal-plane vortices developed during each complete fin stroke period (see Discussion; cf. Table1). Pectoral fin force is the mean reaction force experienced by both left and right paired fins together over the downstroke–upstroke period (from Drucker and Lauder, 1999). (B) Lateral force generated during turning following steady swimming at 0.5Ls^-1. Since turning involves non-periodic fin motion, mean forces are calculated over the duration of the half-stroke. Pectoral force is for the strong-side fin (from Drucker and Lauder, 2001). The substantial contribution of the soft dorsal fin to locomotor force (12% thrust and 35% lateral force) supports an active role for this fin in propulsion. In general, the observed partitioning of force among fins highlights the ability of teleost fishes to use multiple fins simultaneously and independently during locomotion. CM, center of mass of the body (positioned according to Webb and Weihs, 1994).