Effects of bioactive substance from turmeric on growth, skin mucosal immunity and antioxidant factors in common carp, Cyprinus carpio.

Present study evaluated the effects of curcumin, the principal curcuminoid of turmeric, on Cyprinus carpio growth, skin mucosal immune parameters, immune-related gene expression, and susceptibility to pathogen challenge. Diets containing four various concentrations of curcumin (g Kg^-1): 0 g [basal diet], 5 g [T5], 10 g [T10], and 15 g [T15] were fed to the carp (average weight: 16.37 g) for 8 weeks. Growth parameters were analysed at 4 and 8 weeks post-feeding. Skin mucosal immune responses and expression were examined in 8 weeks post-feeding. Growth performance was significantly higher in T10 and T15, with final weight gain of 102.26 ± 2.31 g and specific growth rate of 3.24 ± 0.37, respectively. The lowest feed conversion ratio (2.35 ± 0.16) was recorded in T15 than in the control (P < 0.05). Among the skin mucosal immune parameters examined, lysozyme (36.8 ± 4.03 U mL^-1), total immunoglobulin (6.74 ± 0.5 mg mL^-1), protein level (18.7 ± 1.62 mg mL^-1), alkaline phosphatase (96.37 ± 6.3 IU L^-1), and protease activity (9.47 ± 0.82%) were significantly higher in T15, while the peroxidase activity was higher in T10 (10.24 ± 0.9 U mg^-1 protein). Further, lysozyme, superoxide dismutase (SOD) and catalase (CAT) activities were measured in serum and found to be higher in T10 or T15 than in the control (P < 0.05). However, malondialdehyde level decreased significantly in T10 and T15. Furthermore, antioxidant genes (SOD, CAT, nuclear factor erythroid 2-related factor 2) and anti-inflammatory cytokine Interleukin-10 were upregulated in the head kidney, intestine, and hepatopancreas of fish in T10 and T15. Conversely, expression of pro-inflammatory cytokines (IL-1β, tumour necrosis factor-alpha), signalling molecule NF-κBp65 were down-regulated in the tested tissues of T10 and T15. Expression of Toll-like receptor 22 (TLR22) was down regulated in head-kidney and intestine of T15. Fish from T15 exhibited significantly higher relative post-challenge survival (69.70%) against Aeromonas hydrophila challenge. Results of the present study suggest that dietary supplements of curcumin at 15 g Kg^-1can significantly improve the growth performance, skin mucosal and serum antioxidant parameters, and strengthen the immunity of C. carpio. Therefore, curcumin represents a promising food additive for carps in aquaculture.