Effects of M. oleifera leaf extract on the growth, physiological response and related immune gene expression of crucian carp fingerlings under Aeromonas hydrophila infection.

We evaluated the effect of dietary supplementation with Moringa oleifera leaf extract on the resistance to Aeromonas hydrophila infection in crucian carp. The fish were randomly divided into five groups: the basal diet, the basal diet supplied with 0.25% (0.25 M), 0.5% (0.5 M), 0.75% (0.75 M) and 1.0% M. oleifera leaf extract (1.0 M) for 8 weeks. The growth, antioxidant capabilities, related immune genes as well as resistance to A. hydrophila infection were determined. The results showed that compared with the control group, the weight gain, specific growth rate in the group of 0.5% M. oleifera leaf extract, serum superoxide dismutase (SOD), albumin (ALB) and glutathione peroxidase (GSH-Px), the gene expression of hepatopancreas BTB and CNC homolog 1 (Bach1), NF-E2-related factor 2 (Nrf2), peroxidases (PRX) and NADPH oxidase (NOX) in the group of 0.5%-1.0% M. oleifera leaf extract increased, while feed conversion ratio, serum cortisol, red blood cell (RBC), alanine aminotransferase (ALT), malonaldehyde (MDA) decreased in the group of 0.5%-1.0% M. oleifera leaf extract before the stress. After the infection, the group of 0.5% or 0.75% M. oleifera leaf extract also could improve the serum ALB, hepatopancreas Kelch-like-ECH-associated protein 1 (Keap1), Bach1, Nrf2, TOR, PRX and NOX and reduce cortisol compared with the control group. In summary, this study suggested that 0.5% M. oleifera leaf extract inclusion increased the growth performance, even had positive effects on physiological and immune function, and enhanced resistance against pathogenic infections in crucian carp. The optimum level of M. oleifera leaf extract for crucian carp was estimated to be 0.35%-0.48% based on polynomial comparison with FCR and SGR.