Sodium butyrate suppresses stress, immunosuppression and oxidative stress in common carp, Cyprinus carpio, reared at high stocking density

Organic acid salts can modulate fish growth performance and antioxidant/immune systems, thus they can be used as feed additives for intensive fish culture. Hence, this study investigated the effects of dietary sodium butyrate (NaB) supplementation on growth, antioxidant, immunological and stress indicators in common carp, Cyprinus carpio, reared at high stocking density. Three levels of dietary NaB (0, 1 and 2 g/kg) and two stocking densities [5 (L) and 10 (H) g/L, corresponding to 20 and 40 fish/aquarium, respectively] were combined to have six triplicate treatments: B0-L: 0 g/kg NaB + L; B1-L: 1 g/kg NaB + L; B2-L: 2 g/kg NaB + L; B0-H: 0 g/kg NaB + H; B1-H: 1 g/kg NaB + H; B2-H: 2 g/kg NaB + H. Fish (10.5 +/- 0.17 g) were daily fed at a rate of 3% of biomass for eight weeks. The results showed that NaB contributed to stress mitigation by lowering plasma glucose levels and hepatic transaminases, while increasing plasma triiodothyronine levels. NaB boosted antioxidant capacity by increasing hepatic/intestinal superoxide dismutase, catalase and total antioxidant capacity and lowering malondialdehyde levels. NaB supplementation increased blood leukocyte count, neutrophil percentage, alternative complement activity, mucosal/humoral immunoglobulin levels and mucosal/intestinal lysozyme activities. NaB improved growth performance and feed efficiency, likely due to a reduction in stress and energy expenditure and/or an improvement in overall gut and hepatopancreas health and function. Overall, the inclusion of 1 g/kg NaB in the feed is recommended for optimal health and growth performance of common carp kept at high stocking densities.