ELLERBY, D.J.*; SPIERTS, I.S.Y.; ALTRINGHAM, J.D.: Slow muscle power output of yellow- and silver-phase European eels (Anguilla anguilla, L.): changes in muscle performance prior to migration

The European eel (Anguilla anguilla, L.) has a complex life cycle involving a lengthy spawning migration. The differences in the locomotory demands on different life history stages are considerable. Eels swim in the anguilliform mode in which muscle function has been assumed to be relatively uniform along the body axis relative to other teleosts. The work loop technique was used to determine slow muscle power outputs in yellow (non-migratory) and silver (migratory) life history phases. Swimming kinematics of the two phases were also measured for comparison. Maximum slow muscle power outputs under approximated in vivo conditions were 0.24 Wkg^-1 in yellow-phase eel and 0.74 Wkg^-1 in silver-phase eel. Power output peaked at cycle frequencies of 0.23 to 0.8 Hz. Muscle activation (T_a) and relaxation (T₉₀) times were greater in yellow- than in silver-phase eels. Differences in swimming kinematics and the frequency distribution of tailbeat frequency at a swimming speed of 0.40 BLs^-1 suggested differences in underlying patterns of muscle recruitment between the two life history phases.