MOTOR PATTERNS OF LABRIFORM LOCOMOTION - KINEMATIC AND ELECTROMYOGRAPHIC ANALYSIS OF PECTORAL FIN SWIMMING IN THE LABRID FISH GOMPHOSUS-VARIUS

Labriform locomotion is a widespread swimming mechanism in fishes duri ng which propulsive forces are generated by oscillating the pectoral f ins, We examined the activity of the six major muscles that power the pectoral fin of the bird wrasse Gomphosus varius (Labridae: Perciforme s). The muscles studied included the fin abductors (arrector ventralis , abductor superficialis and abductor profundus) and the fin adductors (arrector dorsalis, adductor superficialis and adductor profundus), O ur goals were to determine the pattern of muscle activity that drives the fins in abduction and adduction cycles during pectoral fin locomot ion, to examine changes in the timing and amplitude of electromyograph ic (EMG) patterns with increases in swimming speed and to correlate EM G patterns with the kinematics of pectoral fin propulsion, EMG data we re recorded from three individuals over a range of swimming speeds fro m 15 to 70 cm s(-1) (1-4.8 TL s(-1), where TL is total body length), T he basic motor pattern of pectoral propulsion is alternating activity of the antagonist abductor and adductor groups, The downstroke is char acterized by activity of the arrector ventralis muscle before the othe r abductors, whereas the upstroke involves nearly synchronous activity of the three adductors, Most EMG variables (duration, onset time, amp litude and integrated area) showed significant correlations with swimm ing speeds, However, the timing and duration of muscle activity are re latively constant across speeds when expressed as a fraction of the st ride period, which decreases with increased velocity. Synchronous reco rdings of kinematic data (maximal abduction and adduction) with EMG da ta revealed that activity in the abductors began after maximal adducti on and that activity in the adductors began nearly synchronously with maximal abduction, Thus, the pectoral fin mechanism of G. varius is ac tivated by positive work from both abductor and adductor muscle groups over most of the range of swimming speeds, The adductors produce some negative work only at the highest swimming velocities, We combine inf ormation from pectoral fin morphology, swimming kinematics and motor p atterns to interpret the musculoskeletal mechanism of pectoral propuls ion in labrid fishes.