| Amount and distribution of red myotomal muscle (RM) in two scombrid fish species were compared and then related to data on swimming performance, muscle biochemistry and swimming kinematics from other studies on the same fish. The kawakawa tuna (Euthynnus affinis, n = 11, 12.2--26.0 cm fork length [FL], 7.19 +/- 1.21 [S.D.]% RM) had a significantly greater amount of red muscle (RM) than chub mackerel (Scomber japonicus, n = 10, 13.1--24.7 cm FL, 5.07 +/- 0.95 [S.D.]% RM). The maximum amount of RM in kawakawa tuna was located anterior to that of the chub mackerel (45% FL versus 65% FL). There were no positive correlations between amount of red muscle and maximum continuous swimming speed, or between whole-animal biochemical indices of aerobic capacity and swimming performance. Therefore, amount of red muscle and biochemical indices are not good predictors of fish activity level. Adult tuna and bonito were dissected to determine whether the distribution of red muscle and tendon geometry is consistent with observed swimming kinematics. Velocity ratios were higher and posterior oblique tendon angles were lower in tunas than in bonitos, which is consistent with observed higher tailbeat frequencies, but not with lower lateral displacement in tunas. |
