Effect of dietary vitamin C on non-specific immunity and mRNA expression of three heat shock proteins (HSPs) in juvenile Megalobrama amblycephala under pH stress

• Immune and anti-oxidative ability were significantly reduced under pH stress.
• Vitamin C has the potential to increase non-immune ability in fish under pH stress.
• Vitamin C has the potential to increase the expression of HSP60 and HSP70 in fish.

This study determined the effect of dietary vitamin C on non-specific immunity and on mRNA expression of three HSPs in juvenile Megalobrama amblycephala under pH stress. Six diets were formulated to contain 0.2, 33.4, 65.8, 133.7, 251.5 and 501.5 mg/kg of vitamin C. Each diet was fed to triplicate groups of fish in cylindrical tanks (220-L, N = 25 fish/tank). After 90 days of feeding, 20 fish per tank were exposed to pH stress (pH ≈ 9.5) for 10 days. Serum alanine aminotransferase (ALT), alkaline phosphatase (ALP), total protein (TP), complement C3 (C3), complement C4 (C4), cortisol, hepatic superoxide dismutase (SOD), antisuperoxide anion free radical (ASAFR), malondialdehyde (MDA) and the relative mRNA expression of heat shock protein 60 (HSP60), 70 (HSP70), and 90 (HSP90) were investigated. The results showed that after pH stress, serum ALP, TP, C3, C4, hepatic SOD, and ASAFR levels were significantly reduced (P < 0.05) while serum ALT, cortisol, hepatic MDA and HSP60 and HSP70 mRNA expression levels were significantly increased (P < 0.05). On the other hand, supplementation with vitamin C significantly reduced levels of serum cortisol (65.8–501.5 mg/kg vitamin C diet groups), ALT (33.4 mg/kg vitamin C diet group) and hepatic MDA (133.7 and 251.5 mg/kg vitamin C diet groups). Supplemented groups had increased serum ALP activity (all treated groups) as well as increased relative mRNA expression of hepatic HSP60 (133.7–501.5 mg/kg vitamin C diet groups) and HSP70 (133.7 and 251.5 mg/kg vitamin C diet groups) (P < 0.05). These results indicate that ingestion of a basal diet supplemented with 133.7–251.5 mg/kg vitamin C could enhance resistance against pH stress in M. amblycephala to some degree.