The mechanical properties of the mantle muscle of European cuttlefish (Sepia officinalis)

The circular muscles surrounding the mantle cavity of European cuttlefish (Sepia officinalis) generate the mechanical power to compress the cavity, forcing a jet of water out of the funnel, propelling the animal during jet propulsion swimming. During ontogeny, jetting frequency decreases in adults compared with juveniles, and this is expected to be reflected in the contractile properties of the locomotory muscles. To develop greater insight into how the locomotion of these animals is powered during ontogeny, we determined the mechanical properties of bundles of muscle fascicles during isometric, isotonic and cyclic length changes in vitro, at two life stages: juveniles and adults. The twitch kinetics were faster in juveniles than in adults (twitch rise time 257 ms compared with 371 ms; half-twitch relaxation 257 ms compared with 677 ms in juveniles and adults, respectively); however, twitch and tetanic stress, the maximum velocity of shortening and curvature of the force–velocity relationship did not differ. Under cyclic conditions, net power exhibited an inverted U-shaped relationship with cycle frequency in both juveniles and adults; the frequency at which maximum net power was achieved was shifted to lower cycle frequencies with increased maturity, which is consistent with the slower contraction and relaxation kinetics in adults compared with juveniles. The cycle frequency at which peak power was achieved during cyclical contractions in vitro was found to match that seen in vivo in juveniles, suggesting power is being maximised during jet propulsion swimming.