Mechanical properties of red and white swimming muscles as a function of the position along the body of the eel Anguilla anguilla

The way in which muscles power steady swimming depends on a number of facto rs, including fibre type and recruitment, muscle strain, stimulation patter n and intensity, and the intrinsic mechanical properties of the muscle fibr es, For a number of undulatory swimming fish species, in vivo studies have shown that muscles at different positions along the body are stimulated dur ing different phases of the strain cycle. Moreover, some intrinsic contract ile properties of the muscles have been found to vary according to their po sition along the body. We report the first results on the mechanical properties of the red and whi te muscles of an anguilliform swimmer, Anguilla anguilla. Small preparation s (0.147-1.335 mg dry mass) were dissected from positions at fractions of 0 .2, 0.4, 0.6 and 0.8 of total body length (BL), We determined the time to 5 0% and 100% peak force and from the last stimulus to 50% relaxation for iso metric contractions; we measured the sarcomere lengths that coincided with in situ resting length, None of these quantities varied significantly with the longitudinal position from which the fibres were taken. We also measure d power and work output during contractions under conditions approximating those used in vivo (cycle frequency, 1Hz; strain amplitude, +/- 10 % L-0, w here Lo is the length giving maximum isometric force). During these experim ents, work output was affected by stimulation phase, but did not depend on the longitudinal position in the body from which the muscles were taken. Our results indicate that red and white eel muscles have uniform properties along the body. In this respect, they differ from the muscle of most non-a nguilliforms, in which muscle kinetics varies in a systematic way along the body. Uniform properties may be beneficial for anguilliform swimmers, in w hich the amplitude of the travelling wave can be pronounced over the entire body length.