ROSENBERGER, L.* J.; WALKER, J. A.; COLLAR, D.; WESTNEAT, M. W.: Effects of fin shape and fin motion on labriform swimming performance

Labriform locomotion in fishes is performed by either rowing or flapping the pectoral fins. In this study, we tested a priori hypotheses of causal associations between fin shape, fin kinematics, and swimming performance using a diverse group of wrasses (Labridae) differing in fin and body shape, swimming behavior, and phylogenetic position, including members of the genera Bodianus, Cheilinus, Choerodon, Coris, Cirrhilabrus, Gomphosus, Halichoeres, Thalassoma, Tautoga, Scarus and others. Locomotor performance was determined as the maximum swimming velocity that fishes attained using strict pectoral-based locomotion. Critical swimming speed ranged from about 3 body lengths per second up to greater than 5 bl/s in the taxa sampled. Fin shape is a major determinant of labriform propulsion mechanics, as wrasses range from extremely paddle-like fins (e.g. Tautogawith an AR of 1.5) to highly tapered and wing-like fins (e.g. Gomphosuswith an AR of 3.5). To assess differences in kinematics of species on the rowing to flapping continuum, we calculated stroke plane angle, frequency and amplitude in all species. Our results show that maximum pectoral-fin-powered swimming speeds were higher in wrasses that had a more vertical stroke plane angle and higher aspect ratio (more wing-like) fins. Recent models suggest that there may be a trade-off between swimming performance and rapid force production for higher maneuverability that may have resulted in repeated evolution of these two alternative strategies in the family Labridae. ONR N000149910184 and NSF DEB- 9815614.