Antioxidant system efficiently protects goldfish gills from Ni2+-induced oxidative stress

► Impact of 96 h exposure to 10, 25 or 50 mg L−1 of Ni2+ on goldfish gills was studied. ► Ni was accumulated in gill as a function of exposure concentrations. ► Carbonyl proteins and lipid peroxides were decreased in gill of Ni-exposed fish. ► Exposure to waterborne Ni triggered the activation of antioxidant enzymes in gills. ► Development of reductive stress in goldfish gills under Ni exposure is suggested.