Kinematics study on pectoral fins of Koi Carp by digital image processing

Attracted by the fact that pectoral fins exhibit complex three-dimensional movements and play very important role in fish maneuvers, a study on Koi Carp is conducted to investigate the kinematics of pectoral fins. In this paper, an efficient high speed photography system is introduced to obtain the double perspective simultaneously, a typical maneuver motion while Koi carp retreating is presented; we discover that the motion of pectoral fin in retreating is an extraordinary complicated three-dimensional pattern. The three-dimensional shape and the maximum bending angle of single fin ray in a fin beat are presented by using digital image processing. Then, we demonstrate the angle of the root of marked fin ray motion in retreating and the correspondence analysis of the surface area of pectoral fin. Finally, three representative motions of pectoral fin: relaxation, expansion and bending are extracted from the three-dimensional grid graph. The results of kinematic of flexible pectoral fins will provide a foundation to mimic a bio-inspired flexible pectoral fin and underwater propeller.