This study explores the effects of supplementing the diets of common carp (Cyprinus carpio) with Spirulina sp. and citric acid (CA) on growth performance and immune parameters. Various experimental diets were formulated, including a control group, diets with 20g/kg Spirulina, 30g/kg Spirulina, 0.5g/kg citric acid, 1.0g/kg citric acid, and four mixed combinations of Spirulina and citric acid. Initially, common carp weighing 15.3 ± 1.9g were fed these diets for eight weeks in 40‐L aquaria with three replicates. Growth performance and immune indices, specifically lysozyme, IgM, and immunoglobulin M (IgM) levels were assessed. The results demonstrated that the Spirulina/citric acid mixture  significantly improved growth performance and immune indices compared to individual Spirulina and citric acid treatments and the control group (P< 0.05). The growth indices indicated increased dietary efficiency with the higher
inclusion of the mixture, with the 30g Spirulina sp. + 1.0g citric acid and 30g Spirulina sp. + 0.5g citric acid treatments exhibiting the highest growth performance and the lowest feed conversion ratio (FCR). In conclusion, dietary supplementation of 30g/kg Spirulina combined with 0.5g/kg citric acid was found to promote growth and positively influence the immune parameters in common carp.