Recent kinematic and hydrodynamic studies on fish median fins have shown that dorsal fins actively produce jets with large lateral forces. Because of the location of dorsal fins above the fishs rol領(lǐng) axis, these lateral forces, if unchecked, would cause fish to roll. In this paper we examine the hydrodynamics of trout anal fin function and hypothesize that anal fins, located below the fishs rol領(lǐng) axis, produce similar jets to the dorsal fin and help balance rol領(lǐng) torques during swimming. We simultaneously quantify the wake generated by dorsal and anal fins in brook trout by swimming fish in two horizontal light sheets filmed by two synchronized high speed cameras during steady swimming and manoeuvring. Six major conclusions emerge from these experiments. 德國LaVision PIV/PLIF粒子成像測速場儀 Imager pro X PIV相機 用于粒子成像測速(PIV)的熒光示蹤粒子