Acts specifically as a negative regulator of skeletal muscle growth. Homodimer; disulfide-linked. Highly expressed in muscle. Also expressed in other tissues such as eye, gill, ovary, gut and brain. Very low level detected in testis. Not expressed in liver, kidney, stomach or heart. Expression increases rapidly in whole body during embryonic and early larval development. However, the rate of expression decreases to plateau during yolk sac absorption. Expression not detected in fertilized oocytes and in prehatching larvae with eye spots. First detected in post-hatching larvae and peaks soon thereafter with the appearance of muscle activity coinciding with early myogenesis. Belongs to the TGF-beta family.