en aquaculture aquaculture پژوهشي Orginal research papers <span lang="TR" style="font-size:11.5pt"><span calibri="" style="font-family:"><span style="color:black">A 2&times;3 factorial design was used to assess the effects of dietary copper (Cu) and selenium (Se) on growth, oxidative stress, and immunity in Beluga sturgeon (<i>Huso huso</i>) juveniles fed optimal and high levels of Mintrex&reg; copper and selenomethionine. Six experimental diets were formulated with two Cu levels (10 and 50 mg Cu kg^-1) and three Se levels (5, 11, and 55 mg Se kg^-1): <a name="_Hlk211423482">Cu₁₀Se₅</a>, Cu₁₀Se₁₁, Cu₁₀Se₅₅, Cu₅₀Se₅, Cu₅₀Se₁₁, and Cu₅₀Se₅₅. Each diet was fed to triplicate groups of 15 fish (initial weight 13.31&plusmn;0.35 g) for 12 weeks. The fish fed with Cu₁₀Se11 diet exhibited the highest weight gain (1092.2&plusmn;11.2%), significantly greater than those fed with Cu₁₀Se₅ (962.2&plusmn;17.3%), Cu₁₀Se₅₅ (928.6&plusmn;33.7%), and Cu₅₀Se₅₅ (721.1&plusmn;46.6%) diets. The best feed conversion ratio was observed in Cu₁₀Se₁₁ (1.24&plusmn;0.05), while the lowest value was in Cu₅₀Se₅₅ (1.81&plusmn;0.16). The protein efficiency ratio was significantly high in Cu₁₀Se11 (1.87&plusmn;0.02) and low in Cu₅₀Se₅₅ (1.28&plusmn;0.16). The hepatic Cu and Se concentrations increased dose-dependently, reaching 38.12&plusmn;2.4 &mu;g g^-1 and 11.68&plusmn;0.8 &mu;g g^-1, respectively, in Cu₅₀Se₅₅. The lowest thiobarbituric acid reactive substances (TBARS) value was recorded in Cu₁₀Se11 (5.83&plusmn;0.56 U mg^-1 protein), while the highest was in Cu₅₀Se₅₅ (11.8&plusmn;0.56 U mg^-1 protein). Antioxidant enzyme activities (CAT, GPx, and Cu-Zn SOD) were significantly reduced in Cu₅₀Se₅₅, whereas IgM (46.1&plusmn;2.65 &micro;g mL⁻&sup1;) and lysozyme (17.7&plusmn;0.95 U mL^-1) values were high in Cu₁₀Se₁₁, but they were markedly suppressed in Cu₅₀Se₅₅ (IgM: 21.4&plusmn;1.09 &micro;g mL⁻&sup1;; lysozyme: 9.9&plusmn;0.74 U mL^-1). Both IgM and lysozyme values were decreased with excess dietary Cu and Se and were negatively correlated with TBARS. These findings indicate that Cu₁₀Se₁₁, containing 10 mg kg^-1Cu and 11 mg kg^-1 Se, optimally enhances growth, reduces oxidative stress, and strengthens immunity in Beluga juveniles, while excessive Cu and Se intake impairs antioxidant capacity and immune functions.</span></span></span> Beluga sturgeon, Cu, Se, Oxidative stress, Antioxidant enzymes, Immunity 215 228 http://jifro.ir/browse.php?a_code=A-10-1274-5&slc_lang=en&sid=1 M. Mohseni mahmoudmohseni73@gmail.com 100319475328460058787 100319475328460058787 Yes International Sturgeon Research Institute, Iranian Fisheries Science Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Rasht, Iran Sungchul C. Bai scbai@pknu.ac.kr 100319475328460058788 100319475328460058788 No Department of Marine Bio-materials and Aquaculture/Feeds and Foods Nutrition Research Center (FFNRC), Pukyong National University, Busan 608-737, Rep of Korea R.A. Ozorio rodrigo.ozorio@ciimar.up.pt 100319475328460058789 100319475328460058789 No CIIMAR, Terminal de Cruzeiros do Porto de Leixões, Av. General Norton de Matos s/n, 4450-208, Matosinhos, Portugal F. Fadakar Masouleh fadakarfatemeh62@gmail.com 100319475328460058790 100319475328460058790 No International Sturgeon Research Institute, Iranian Fisheries Science Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Rasht, Iran