TYTELL, E.D.*; LAUDER, G.V.: Multiple escape response patterns in Polypterus senegalus: Kinematics and electromyography

The kinematics and muscle activity patterns of escape responses in the bichir, Polypterus senegalus, were analyzed using high speed video and electromyography (EMG). Five fish were filmed at 250Hz while recording white muscle activity at five sites on both sides of the body. Body wave speed and center of mass velocity, acceleration, and curvature were calculated from digitized outlines. Six EMG variables per channel were also calculated to characterize the motor pattern. In contrast to previous studies, which observed mostly uniform escape responses, P. senegalus shows a wide range of patterns. All patterns have the characteristic simultaneous onset of ipsilateral muscle activity, but they vary greatly in both kinematics and EMGs. In the most vigorous turns, the head often touches the tail, velocity and acceleration are high, stage I activity is long and strong, but the muscles often have little stage II activity. In the least vigorous turns, maximum body curvature, velocity, and acceleration are low, stage I is short and weak, but stage II is relatively stronger. There seems to be a continuum of escape responses between these extremes. None of the 59 observed escape responses have simultaneous, equal amplitude muscle activity along both sides of the body, as previously postulated. Instead, ipsilateral activity on the anterior third of the body is unopposed by contralateral activity. Posteriorly, though, contralateral and ipsilateral muscles are active simultaneously at about the same amplitude. The difference in activity along the body suggests that anterior ipsilateral muscles initiate a wave of bending that is propagated passively along the body. Posterior muscles stiffen the body, increasing this body wave velocity, but do not contribute to the bending directly.