This study aimed to investigate the effects of different levels of reused water on serum biochemical and immunological indices of beluga (Huso huso) in a recirculating aquaculture system. The experiment was conducted in a completely randomized design with three treatments: R0 (100% fresh water), R50 (50% recycled water), and R80 (80% recycled water), each with three replicates. A total of 180 beluga sturgeons with an average initial weight of 6162.71 ± 68.66 g were reared for eight months in nine circular tanks with a volume of 18 m³ each. The results showed that total protein and albumin levels were significantly higher in the R80 treatment compared to other groups, while serum glucose, total lipid, and cholesterol were significantly higher in R0. Hepatic enzyme activities (ALT and AST) were significantly elevated in R80 compared to R0, whereas no significant differences were observed between R50 and R0. LDH levels were lower in R50 and R80 than in R0. Regarding immune parameters, lysozyme activity, immunoglobulin M (IgM) levels, and complement activity (ACH50) were significantly higher in R80 compared to R0; however, IgM differences between the reused water treatments were not statistically significant. Overall, the use of 80% reused water in the recirculating system improved serum biochemical and immune parameters, contributing to more efficient water resource utilization in beluga aquaculture.