Protects cells and enzymes from oxidative damage, by catalyzing the reduction of hydrogen peroxide, lipid peroxides and organic hydroperoxide, by glutathione (By similarity). May defend against reactive oxygen species that accumulate during the immune response. 2 glutathione + H2O2 = glutathione disulfide + 2 H2O Expressed at high levels in the ovary and at lower levels in the gill and hepatopancreas. Not detected in heart, brain, thoracic ganglia, gut, muscle, epidermis or testis. Expressed strongly in fertilized eggs; expression decreases significantly during the cleavage stage and is barely detectable in subsequent stages of embryogenesis. Up-regulated in hepatopancreas following bacterial or viral infection. Belongs to the glutathione peroxidase family.