Current results also show that the region of flatfish MSTNpro consisting of 45–65 (Pep45-65) can suppress mouse MSTN activity and increase muscle mass and function without invoking an immune response, implying that Pep45-65 would be a potential agent to enhance skeletal muscle growth and function in animals or to treat muscle atrophy caused by various clinical conditions. This evidence concerns the gene MSTN and muscle atrophy.