QUANTITATIVE DISTRIBUTION OF MUSCLE-FIBER TYPES IN THE SCUP STENOTOMUS CHRYSOPS

Because the mass-specific power generated by myotomal muscle during sw imming varies along the length of the fish, a realistic assessment of total power generation by the musculature requires integrating the pro duct of mass-specific power and muscle mass at each position over the length of the fish. As a first step toward this goal, we examined the distribution of red, pink, and white muscle along the length of Stenot omus chrysops (scup) using histochemical and image analysis techniques . The largest cross-sectional area of red fibers occurs at 60% of tota l fish length and declines both anteriorly and posteriorly. By contras t, white fibers have the largest cross-sectional area in the anterior and decline dramatically moving posteriorly. The proportion of the fis hes' cross-section occupied by red fibers increases from 1.37% to 8.42 % moving posteriorly along the length of the fish. In contrast, the pr oportion of cross-sectional area occupied by pink fibers is constant ( 1.19%), while the proportional cross-sectional area of white fibers fa lls from 82.5% to 66.3%. The red, pink, and white fibers comprise 2.09 , 0.73, and 51.1%, respectively, of total fish weight. We also compare d the distribution of muscle in 10 degrees C- and 20 degrees C-acclima ted animals. The value for red fiber volume, though slightly higher (1 3%) in cold-acclimated fish, is not statistically different. No differ ence was found in pink or white fibers. Finally, the finding that most of the red muscle is in the posterior half of the fish further suppor ts the notion that most power for steady swimming at moderate speeds c omes from posterior rather than anterior musculature. (C) 1996 Wiley-L iss, Inc.