THE ROLES OF PINK AND RED MUSCLE IN POWERING STEADY SWIMMING IN SCUP,STENOTOMUS CHRYSOPS

Fishes power steady, undulatory swimming using both red and pink muscl e. In this study we examined the roles of the two fiber types in gener ating power for swimming by using a two-step technique. First, in vice data is collected from swimming fish, and second, the electrical acti vity and muscle length change conditions recorded in vivo are recreate d in vitro with isolated muscle bundles, Force production and power ge neration by muscle during swimming can then be estimated. In scup, bot h red and pink muscle are recruited to power swimming at the maximum s ustained swimming speed. For both fiber types, the duration of electri cal activity decreases from anterior to posterior. However the amplitu de of muscle length change increases anterior to posterior. Mass-speci fic power production increases posteriorly for both muscle types. The faster contraction kinetics of pink muscle translate to higher power p roduction by pink muscle relative to red muscle for all longitudinal p ositions of the fish. Determination of absolute power production based on mass-specific power and muscle mass, shows that the posterior regi ons of the fish generate the most power for swimming. At 20 degrees C, red muscle generates more absolute power than pink due to its higher muscle mass. However, at 10 degrees C, pink muscle generates more abso lute power than red, because red muscle produces little or no positive power for all longitudinal positions.