The functional design of swimming muscles in fish

The trunk muscles in fish are arranged in a series of myomeres, separated by folded myosepta with tendons and (in bony fish) bones. The muscle fibres are arranged in complex 3D patterns. The orientation of muscle fibres varies with the position in the trunk muscles. A series of mechanical models will be reviewed that are designed to explain the functional relevance of several architectural features. Mechanical stability and force transmission demands explain (at least partially) the myomere shape and the location and orientation of tendons and bones. The muscle fibre orientations are explained by demands of work output at different swimming intensities and a high power density of the muscle tissue during strenuous activities. Similar functional demands have led to disjunctive solutions in lampreys, selachians and teleosts. Superfast muscles are required to drive the high-frequency swimming motions in larval teleosts. The muscle fibre reorientation during development in teleosts is probably driven by the local mechanical conditions.