Bioinspiration From Flexible Propulsors: Organismal Design, Mechanical Properties, Kinematics and Neurobiology of Pectoral Fins in Labrid Fishes

Abstract

AbstractLabrid fishes use their pectoral fins for efficient high-speed cruising behavior, as well as for precision maneuvering in complex environments, making them good models for biomimicry applications in propulsor technology for aquatic vehicles. Lift-based labriform locomotion is a form of aquatic flight used by many species and is the sole mode of transport across most speeds by some of the largest wrasses and parrotfishes on coral reefs. Although basic and applied research has explored fin design in several species utilizing labriform propulsion, a detailed analysis of fin anatomy, fin mechanical properties, and well-resolved three-dimensional (3D) kinematics in high-performance aquatic flyers has not yet been attained. Here, we present recent research on fin structure, fin flexural stiffness, sensory abilities of fins, and a novel 3D approach to flexible fin kinematics. Our aims are to outline important future directions for this field and to assist engineers attempting biomimicry of maneuverable fin-based locomotion for applications in robotics. First, we illustrate the anatomical structure and branching patterns of the pectoral fin skeleton and the muscles that drive fin motion. Second, we present data on the flexural stiffness of pectoral fins in the parrotfish (Scarus quoyi), setting up a stiffness field that gives the fin propulsor its passive mechanical properties and enables hydrodynamically advantageous fin deformations during swimming. Third, we present 3D reconstructions of the kinematics of high-performance Scarus fins that greatly enhance our ability to reproduce fin motions for engineering applications and also yield insight into the functional role of the fin stiffness field. Lastly, recent work on mechanosensation is illustrated as key to understanding sensorimotor control of labriform locomotion. Research on pectoral fin structure, function, and neural control in large marine species with high-performance wing-like fins is important to the comparative biology of locomotion in fishes, and we suggest it is a productive area of research on fin function for applications in the design of quiet, efficient propulsors.