Effects of dietary malic acid and ginger powder supplementation on growth, immunity, antioxidant status, and disease resistance in grass carp (Ctenopharyngodon idella)

The present study investigated the effect of dietary supplements of malic acid (MA) and ginger powder ( Zingiber officinale ) (GP), individually and in combination, on the growth and health status of grass carp ( Ctenopharyngodon idella ). Fish with initial body weight of 4.4 ± 0.01 g were allocated to four treatments with three replicates and were fed with an un-supplemented diet (control, T0), 0.25% MA (T1), 0.2% GP (T2), and combination of both elements (0.25% MA + 0.2% GP, T3) for 8 weeks then were challenged with Aeromonas hydrophila infection. The results showed that the T1, T2 and T3 treatments exhibited significantly higher values for final weight (FW) as compared to the T0 (P < 0.05). A notable reduction was observed in triglyceride level in fish fed supplemented diets (P < 0.05). The addition of MA and GP did not yield any significant impact on the content of the urea (P > 0.05). Immunoglobulin, total immunoglobulin, and lysozyme levels were significantly higher in the T1, T2, and T3 compared to the T0 (P < 0.05). Serum antioxidant enzymes including glutathione peroxidase (GPX), superoxide dismutase (SOD), catalase (CAT) significantly increased in supplemented diets and they were notably higher in T2 and T3 ( P  < 0.05). Immune-related genes ( IL6, IL10 ) and antioxidant related gene ( CAT, GPX ) were upregulated in T1, T2 and T3 compared to T0 (p < 0.05). The highest mortality rates following a challenge with A. hydrophila were seen in T0. In conclusion, dietary supplementation with 0.25% malic acid (MA) and 0.2% ginger powder optimally enhances grass carp growth, immunity, and disease resistance, offering a natural alternatives to antibiotics in sustainable aquaculture.