Quantifying the unsteady flow structures produced by swimming fishes represents a difficult task because direct measurements applied to water environment are not possible. However, using 3D PTV(Particle Tracking Velocimetry), it is possible quantify the effect of fish fins on water movement. We used 3D PTV to visualize water flow in the wake of the pectoral fin of goldfish. Swimming speed is 0.0378m/s. Velocity quantified in three dimensional reconstruction of vortex structures. Vorticity is spouted out by each fin while the fin is a rotary motion. Left and right vortex produced by each fin are predicted to help maneuverability and body balance.