KINEMATIC AND ELECTROMYOGRAPHIC ANALYSIS OF PECTORAL FIN LOCOMOTION IN TWO SPECIES OF SURFPERCH.

E.G. Drucker* and J.S. Jensen. Harvard University, Cambridge, MA. American Society of Zoologists, 1993 Annual Meeting.

Surfperches (Embiotocidae) rely exclusively on the pectoral fins for propulsion over a wide range of swimming speeds. We compared patterns of pectoral fin movement and muscle activity during steady labriform locomotion in two distantly related surfperches, Amphistichus rhodoterus, a species found in open, unstructured habitats, and Embiotoca lateralis, a species occurring in complex, structured habitats. To study the kinematics of the fins we simultaneously videotaped (60 fps) the dorsal and lateral aspects of surfperches swimming in a flume at speeds ranging from 0.3 to 3.0 standard lengths/sec. We synchronously recorded electromyograms from six pectoral muscles in order to examine the neuromuscular control of fin movements. For both A. rhodoterus and E. lateralis pectoral fin beat frequency increased with swimming speed. Above approximately 2.0 pectoral fin beats/sec both species switched from exclusively pectoral fin locomotion to pectoral + caudal fin undulation. A. rhodoterus was able to maintain a higher swimming speed at a given fin beat frequency than E. lateralis, and consequently began to employ caudal locomotion at a higher speed (2.2 lengths/sec, as compared to 1.8 lengths/sec for E. lateralis). The number of muscles recruited and the amplitude of their activity increased with swimming speed in both species, yet the sequence of muscle contractions during the fin beat cycle was invariant. Ecologically and evolutionarily divergent surfperches thus swim using a conserved motor program. Differences in steady swimming performance among surfperches appear to stem from differences in the architecture of the pectoral fin rather than from variation in the temporal pattern of muscle activity.