Mechanical Properties of the Myotomal Musculo-Skeletal System of Rainbow Trout, Salmo Gairdneri

Net forces and velocities resulting from in situ contractions of the myotomal musculature on one side of the body were measured at the hypural bones. Forces, velocities and power were determined with the body bent into a range of postures typical of those observed during fast-start swimming. For trout averaging 0.178 m in length and 0.0605 kg in body mass, the muscle system exerts a maximum normal force of 2.2N at the base of the caudal fin. This force is equivalent to 11.8 kN m-2 based on the mean cross-sectional area of the myotomal muscle. The maximum velocity was 1.11 m s-1, and the maximum mechanical power output, 0.64 W, or 42.4 W kg-1 muscle. Based on estimates of swimming resistance, these results would suggest acceleration rates of 7.5 to 16.5 m s-2, similar to averages observed during fast-starts. Maximum sprint speeds would range from 6.5 to 17.8 body lengths s-1, spanning the range of maximum speeds reported in the literature. It is suggested that maximum speed is limited by interactions between muscle contraction frequency and endurance. Losses in the mechanical linkages between muscle fibres and propulsive surfaces were estimated at about 50% for power with possibly greater losses in force transmission. Maximum force and power did not vary over the range of postures tested, supporting Alexander's (1969) suggestions that white muscle should contract over a small portion of the resting length of the fibres.