dietary organic copper and selenium interactions in juvenile beluga sturgeon (huso huso): effect on growth, oxidative stress, and immunity

A 2×3 factorial design was used to assess the effects of dietary copper (cu) and selenium (se) on growth, oxidative stress, and immunity in beluga sturgeon (huso huso) juveniles fed optimal and high levels of mintrex® 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): cu10se5, cu10se11, cu10se55, cu50se5, cu50se11, and cu50se55. each diet was fed to triplicate groups of 15 fish (initial weight 13.31±0.35 g) for 12 weeks. the fish fed with cu10se11 diet exhibited the highest weight gain (1092.2±11.2%), significantly greater than those fed with cu10se5 (962.2±17.3%), cu10se55 (928.6±33.7%), and cu50se55 (721.1±46.6%) diets. the best feed conversion ratio was observed in cu10se11 (1.24±0.05), while the lowest value was in cu50se55 (1.81±0.16). the protein efficiency ratio was significantly high in cu10se11 (1.87±0.02) and low in cu50se55 (1.28±0.16). the hepatic cu and se concentrations increased dose-dependently, reaching 38.12±2.4 μg g^-1 and 11.68±0.8 μg g^-1, respectively, in cu50se55. the lowest thiobarbituric acid reactive substances (tbars) value was recorded in cu10se11 (5.83±0.56 u mg-1 protein), while the highest was in cu50se55 (11.8±0.56 u mg-1 protein). antioxidant enzyme activities (cat, gpx, and cu-zn sod) were significantly reduced in cu50se55, whereas igm (46.1±2.65 µg ml⁻¹) and lysozyme (17.7±0.95 u ml-1) values were high in cu10se11, but they were markedly suppressed in cu50se55 (igm: 21.4±1.09 µg ml⁻¹; lysozyme: 9.9±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.