This study was conducted to evaluate the relative bioavailability of copper sulfate (CuSO4), copper-methionine (CuMet) and nano‑copper oxide (CuONano) as a diet additive by comparing growth, Cu status, antioxidant activity, immune response and Cu apparent digestibility in Russian sturgeon Acipenser gueldenstaedtii. The control was a semi-purified basal diet without Cu supplementation and the experimental diets were prepared with the forms of CuSO4, CuMet and CuONano, representatively. The Cu contents were 2, 4, 6, 8 and 16 mg/kg in the CuMet and CuONano diet groups, and 4, 6 and 16 mg/kg in the CuSO4 diet groups. Sturgeon (9.82 ± 0.08 g) were fed with the control diet and 13 experimental diets with Cu in different contents and sources for 8 weeks. The bacterial challenge test and Cu apparent digestibility determination were carried out at the end. The highest weight gain (WG), whole body Cu concentration, Cu apparent digestibility, copper‑zinc superoxide dismutase (Cu-Zn SOD) activity, total antioxidant capacity, lysozyme and immunoglobulin M content were achieved at 6 mg Cu/kg in the CuSO4 diet, and 4 mg Cu/kg in both CuMet and CuONano diets. Sturgeon fed 4 mg Cu/kg in the CuMet diet or the CuONano diet had higher growth rate, tissue Cu deposition, antioxidant and immune capacity than fish fed the same Cu content in the CuSO4 diet. At the same time, Cu in the CuMet or CuONano diet exhibited higher apparent digestibility and Aeromonas hydrophila resistance. When the Cu content was standardized in the form of CuSO4, the relative Cu bioavailability was 153% - 168% in the CuMet diet and 172% - 202% in the CuONano diet based on weight gain, hepatic Cu[sbnd]Zn SOD activity, and whole body Cu concentrations. The optimal dietary Cu requirements was about 5 mg/kg when CuMet or CuONano was used, and increased to 8 mg/kg when CuSO4 was used. This study indicates that Cu in the forms of CuMet and CuONano is 1.5–2 times more bioavailable than in the form of CuSO4 for the dietary Cu requirements of Russian sturgeon.