Hydrodynamics of suckermouth catfish: The role of wake forces during the fast start

Abstract

Suckermouth catfish have a unique tail shape with an upturned caudal peduncle and a ventral lobe of the caudal fin that is longer than the dorsal lobe. We visualized the wake flows of four suckermouth catfish (Peterygophichthys gibbiceps) using particle image velocimetry and analyzed the effect of these tail features on their fast-starting behavior. In this study, we measured the jet and ring axis angles of vortex rings generated by suckermouth catfish during a 1.9 body lengths per second (BL s−1) fast start, and recorded their corresponding body, path and tail angles. The results showed that the suckermouth catfish produced an average jet angle of 47.4° despite a mean tail angle of about 20.7° during fast starts. In addition, further studies included evaluating the positional relationship between force and the center of mass of suckermouth catfish and analyzing the balance of forces and moments required by suckermouth catfish during starting in conjunction with the measured fish body density. During fast starts and escapes, the suckermouth catfish can actively control its tail to change the direction of the force and the pitching moment to improve its maneuverability and stability. This study may provide inspiration for the design of new bionic underwater robots and swimming control strategies.