Acts specifically as a negative regulator of skeletal muscle growth. Homodimer; disulfide-linked. Highly expressed in muscle (PubMed:20483295, PubMed:17048071). Also expressed in other tissues such as eye, brain, gill, heart, head kidney, stomach and intestine. Low levels in spleen and liver (PubMed:17048071). Low levels detected in the unfertilized eggs, newly fertilized eggs, 16-cell stage and morula stage embryos. Higher levels detected in the blastula, gastrula and neurula stages. Higher levels also detected during the lens formation stage, somite and hatching stage. The expression levels continue to increase during development and peaks at 30 day old larvae, and then gradually decreases to lower levels again in day 60 larval stage. (Microbial infection) Myostatin concentrations are decreased in serum of fish infected with nodavirus as compared to serum from uninfected fish (at protein level). Belongs to the TGF-beta family.