RED AND WHITE MUSCLE-ACTIVITY AND KINEMATICS OF THE ESCAPE RESPONSE OF THE BLUEGILL SUNFISH DURING SWIMMING

We quantified midline kinematics with synchronized electromyograms (em gs) from the red and white muscles on both sides of bluegill sunfish ( Lepomis macrochirus) during escape behaviors which were elicited from fish both at a standstill and during steady speed swimming. Analyses o f variance determined whether or not kinematic and emg variables diffe red significantly between muscle fiber types, among longitudinal posit ions, and between swimming versus standstill trials. At a given longit udinal location, both the red and white muscle were usually activated synchronously during both stages of the escape behavior. Stage 1 emg o nsets were synchronous; however, the mean durations of stage 1 emgs sh owed a significant increase posteriorly from about 11 to 15 ms. Stage 2 emgs had significant posterior propagation, but the duration of the stage 2 emgs was constant (17 ms). Posterior emgs from both stages occ urred during lengthening of the contractile tissue (as indicated by la teral bending). Steady swimming activity was confined to red muscle bu rsts which were propagated posteriorly and had significant posterior d ecrease in duration from about 50% to 37% of a cycle. Fish performed e scape responses during all phases of the steady swimming motor pattern . All kinematic events were propagated posteriorly. Furthermore, no di stinct kinematic event corresponded to the time intervals of the stage 1 and 2 emgs. The rate of propagation of kinematic events was always slower than that of the muscle activity. The phase relationship betwee n lateral displacement and lateral bending also changed along the leng th of the fish. Escape responses performed during swimming averaged sm aller amplitudes of stage 2 posterior lateral displacement; however, m ost other kinematic and emg variables did not vary significantly betwe en these two treatments.