Acts specifically as a negative regulator of skeletal muscle growth. May down-regulate muscle-specific transcription factors such as myod and myog. Homodimer; disulfide-linked. Predominantly expressed in muscle. At hatching, expression is strongest in the skin epithelium, and is also found in the retina and brain. From day 28, expressed in skeletal muscle. In the adult, highest expression is seen in the gastrointestinal tract, brain, muscle, heart and testis. Also expressed in the adult pharynx, kidney, spleen, liver, gill, eyes, skin, swim bladder and ovary. Expressed both maternally and zygotically. Weakly expressed ubiquitously in early stage embryos. Present transiently in the blastula with levels dropping almost completely during gastrulation. Expression peaks during late somitogenesis, decreases at the end of somitogenesis, and then rises again at and after hatching. Strongly expressed in swimming larvae, juveniles and adults. Repressed in adult muscle, and stimulated in adult spleen, when fish are grown in overcrowded conditions. Defects produce a giant phenotype. Belongs to the TGF-beta family.