RED MUSCLE MOTOR PATTERNS DURING STEADY SWIMMING IN LARGEMOUTH BASS -EFFECTS OF SPEED AND CORRELATIONS WITH AXIAL KINEMATICS

We analyzed midline kinematics and obtained electromyograms (EMGs) fro m the superficial red muscle at seven longitudinal positions in four l argemouth bass swimming steadily at standardized speeds of 0.7, 1.2, 1 .6, 2.0 and 2.4 lengths s(-1), Analysis of variance was used to test f or significant variation attributable to both speed and longitudinal p osition, EMGs propagated posteriorly were unilateral and alternated be tween the left and right sides, Despite the propagation of EMGs, all t he red muscle along an entire side of the fish was simultaneously acti ve for as much as one-quarter of the locomotor cycle, When expressed a s a proportion of the locomotor cycle, EMG durations at a given site d id not vary significantly with speed but did vary longitudinally, rang ing from values of 0.45 cycles anteriorly to 0.35 cycles posteriorly, The amplitudes of lateral displacement and bending depended on longitu dinal position and also increased by a maximum of approximately 50 % w ith increased swimming speed, whereas for all longitudinal positions t he intensity of EMGs increased approximately fourfold with increased s wimming speed, Electrical activity of red muscle did not correspond si mply to the time of muscle shortening. Instead, the timing of EMG onse t and offset relative to both lateral bending and displacement changed significantly with both longitudinal position and increased speed, su ch that the phase shifts between the EMGs and kinematic values were ge nerally greatest for posterior sites at the fastest speeds, At a singl e longitudinal position, the phase shift between the EMG and maximal l ateral bending could change by more than one-tenth of a cycle from the slowest to the fastest swimming speed, Phase lags per body segment of EMG onset and EMG offset did not vary significantly with either swimm ing speed or longitudinal position, EMG offset was propagated posterio rly faster than EMG onset, and both EMG onset and EMG offset were gene rally propagated faster than both lateral bending and displacement, La rgemouth bass have a similar number of vertebrae to carp, and these tw o species also have a very similar pattern of muscle activation that d iffers substantially from that of the trout, which has nearly twice as many vertebrae.