The snake fish red muscle fiber, consisting of only polygonal myofibrils, has a smaller diameter and more abundant mitochondria and glycogen granules than the white fiber, which consists of ribbon-like and polygonal myofibrils. M bands, ordered Z bands, well developed triads, and multiple neuromuscular junctions of 'en grappe' type, which lack postsynaptic infoldings, occur in both types of fiber. The density of neuromuscular junctions is greater in the red fiber than in the white fiber. These results indicate that the both types of fiber of the snake fish are morphologically different from the slow and twitch fibers of the frog.