© 1996 by The Society for Integrative and Comparative Biology
Functional Morphology of Aquatic Flight in Fishes: Kinematics, Electromyography, and Mechanical Modeling of Labriform Locomotion1
Department of Zoology, Field Museum of Natural History Roosevelt Road at Lake Shore Drive, Chicago, Illinois 60605
Labriform locomotion is the primary swimming mode for many fishes that use the pectoral fins to generate thrust across a broad range of speeds. A review of the literature on hydrodynamics, kinematics, and morphology of pectoral fin mechanisms in fishes reveals that we lack several kinds of morphological and kinematic data that are critical for understanding thrust generation in this mode, particularly at higher velocities. Several needs include detailed three-dimensional kinematic data on species that are pectoral fin swimmers across a broad range of speeds, data on the motor patterns of pectoral fin muscles, and the development of a mechanical model of pectoral fin functional morphology. New data are presented here on pectoral fin locomotion in Gomphosus varius, a labrid fish that uses the pectoral fins at speeds of 1 –6 total body lengths per second. Three-dimensional kinematic data for the pectoral fins of G. varius show that a typical "drag-based" mechanism is not used in this species. Instead, the thrust mechanics of this fish are dominated by lift forces and acceleration reaction forces. The fin is twisted like a propeller during the fin stroke, so that angles of attack are variable along the fin length. Electromyographic data on six fin muscles indicate the sequence of muscle activity that produces antagonistic fin abduction and adduction and controls the leading edge of the fin. EMG activity in abductors and adductors is synchronous with the start of abduction and adduction, respectively, so that muscle mechanics actuate the fin with positive work. A mechanical model of the pectoral fin is proposed in which fin morphometrics and computer simulations allow predictions of fin kinematics in three dimensions. The transmission of force and motion to the leading edge of the fin depends on the mechanical advantage of fin ray levers. An integrative program of research is suggested that will synthesize data on morphology, physiology, kinematics, and hydrodynamics to understand the mechanics of pectoral fin swimming.