Disulfide reductase. May participate in various redox reactions through the reversible oxidation of its active center dithiol to a disulfide and catalyze dithiol-disulfide exchange reactions (PubMed:23994424). Has peroxidase activity and may contribute to the elimination of cellular hydrogen peroxide (By similarity). May function as an antioxidant involved in response to viral infection (PubMed:23994424). Predominantly expressed in liver, brain and muscle. Also expressed in kidney, intestine, skin, stomach, gill and head kidney. Up-regulated in liver in response to Singapore grouper iridovirus (SGIV) infection. 2.8-fold induction after 8 h injection of SGIV and the expression increases up to about 70-fold at 72 hours post injection, then decreases to about 26-fold at 120 h. Belongs to the thioredoxin family.