CONTRACTION DYNAMICS AND POWER PRODUCTION OF PINK MUSCLE OF THE SCUP (STENOTOMUS CHRYSOPS)

Although the contribution of red muscle to sustained swimming in fish has been studied in detail in recent years, the role of pink myotomal muscle has not received attention. Pink myotomal muscle in the scup (S tenotomus chrysops) lies just medial to red muscle, has the same longi tudinal fibre orientation and is recruited along with the red muscle d uring steady sustainable swimming. However, pink muscle has significan tly faster rates of relaxation, and the maximum velocity of shortening of pink muscle (7.26+/-0.18 muscle lengths s(-1), N=9, at 20 degrees C, and 4.46+/-0.15 muscle lengths s(-1), N=6, at 10 degrees C; mean +/ - S.E.M.) is significantly faster than that of red muscle. These prope rties facilitate higher mass-specific maximum oscillatory power produc tion relative to that of red muscle at frequencies similar to the tail beat frequency at maximum sustained swimming speeds in scup. Additiona lly, pink muscle is found in anatomical positions in which red muscle produces very little power during swimming: the anterior region of the fish, which undergoes the lowest strain during swimming. Pink muscle produces more oscillatory power than red muscle under low-strain condi tions (+/-2-3 %) and this may allow pink muscle to supplement the rela tively low power generated by red muscle in the anterior regions of sw imming scup.