Morphometric and Histochemical Characteristics of Fiber Types in Trunk Muscle of Mullet, Mugil cephalus

Histochemical and morphometric approaches were applied to identify muscle fiber types of each muscle patterns. Fiber types in trunk muscle of the mullet, Mugil cephalus, were classified and reported in the present study. Muscle fiber types in each muscle pattern were identified by histochemical characteristics of ATPase, NADH-TR, LDH, and glycogen and lipid contents. The white muscle had one fiber type (IIb) which had a large cross-sectional area (CSA: 3143.69 ± 1870.69 μm^2). Both pink and red muscle are heterogenous containing 3 muscle fiber types (I, IIb, IIc) with varying proportion. Red muscle was composed of 60% type I fibers (637.36 ± 203.03 μm^2), 30% type IIc fibers (112.41 ± 75.89 μm^2) and less than 5% type IIb fibers (978.51 ± 322.05 μm^2), while pink muscle composed of 40% type I fibers (673.17 ± 263.05 μm^2), 50% type IIc fibers (150.43 ± 131.46 μm^2), and less than 10% type IIb fibers (2156.28 ± 636.12 μm^2). Differences in the muscle fiber type composition are attributed to adaptations for improved efficiency of the swimming performance for the different behavioural functions.