On the design of fish myotomal muscles

Abstract

The physiology of fish myotomal muscle is reviewed and discussed in relation to swimming behavior. Slow muscle fibers are arranged in parallel to the longitudinal body axis whereas fast fibers make varying angles of up to 40.degree.. This pattern of organization enables individual fast fibers to produce large bending moments in the trunk for almost isometric contractions (7-9% resting length for elasmobranchs and 2-3% resting length for teleosts). There is an orderly recruitment of slow red > fast red > fast white fibers with increasing swimming speed. The tail-beat frequency required to produce maximum speed varies inversely with body-length. Larvae and small fish have tail-beat frequencies up to 60 Hz. Adaptations for rapid cycles of contraction in fast muscles include an extensive sarcoplasmic reticulum and high concentrations (.apprx. 1 mM) of cytoplasmic Ca2+-binding proteins.