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

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 degreesC. Curvatures and accelerations of mid-body axes were calculated from digitised outlines. Maximum accelerations at 0.3 FL (fork length) from the snout were 54 m s-2 for C-starts and 40 m s-2 for S-starts. The total turning angle was approximately 150 degrees in C-starts. This angle was 70 degrees during escape S-starts, significantly 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 anterior fibres (red 27 %; white 16 %). During S-starts, however, maximum strains in anterior fibres (red 39 %; white 24 %) were more than twice those in posterior fibres (red 17 %; white 10 %). In a C-start, the fish made a large turning angle directed away from the stimulus by bending its tail strongly and thereby producing a large thrust. A larger anterior peak curvature of the fish during S-starts enabled the carp to control the direction of escape better than during C-starts, but with lower accelerations and smaller turning angles. During cyclic and intermittent swimming, red posterior fibres experienced the largest strains. Interestingly, previous studies have shown these fibres to have the lowest passive stiffness and the largest titin isoform, allowing them to attain large strain amplitudes with relatively low passive tensions.