Deep-sea fishes, Coryphaenoides armatus and C. yaquinae, have three unique amino acid substitutions, V54 or L67P, Q137K and A155S, in comparison with non-deep sea fish, C. acrolepis. The V54A or L67P substitution plays an important role in actin polymerization under high pressures. The myosin heavy chain from deep-sea fishes has one amino acid deletion in the loop-2 region, which is one of actin-binding sites. However, the role of this deletion has remained unclear.