Kinematics and muscle dynamics of C- and S-starts of carp (Cyprinus carpioL.)

An analysis is presented of body curvature, acceleration and muscle strain during fast-starts in the common carp (Cyprinus carpio L.). C- and S-starts were filmed at 200 frames s(-1) at 23 degrees C, Curvatures and accelerati ons of mid-body axes were calculated from digitised outlines. Maximum accel erations at 0.3 FL (fork length) from the snout were 54 m s(-2) for C-start s and 40 m s(-2) for S-starts, The total turning angle was approximately 15 0 degrees in C-starts. This angle was 70 degrees during escape S-starts, si gnificantly larger than for predatory S-starts in other species. Sarcomere strains of axial muscle fibres were calculated at 0.4 and 0.8 FL. During C- starts, white muscle fibres were exposed to maximum sarcomere strains of up to approximately 16 %, and posterior fibres had similar strains to anterio r fibres (red 27 %; white 16 %). During S-starts, however, maximum strains in anterior fibres (red 39 %; white 24 %) were more than twice those in pos terior fibres (red 17 %; white 10 %), In a C-start, the fish made a large t urning angle directed away from the stimulus by bending its tail strongly a nd thereby producing a large thrust. A larger anterior peak curvature of th e fish during S-starts enabled the carp to control the direction of escape better than during C-starts, but with lower accelerations and smaller turni ng angles. During cyclic and intermittent swimming, red posterior fibres ex perienced the largest strains. Interestingly, previous studies have shown t hese fibres to have the lowest passive stiffness and the largest titin isof orm, allowing them to attain large strain amplitudes with relatively low pa ssive tensions.