Abstract:The purpose of this study was to investigate the effects of dietary vitamin C on the immunity, antioxidant capacity, and stress tolerance of juvenile Lateolabrax maculatus under acute cooling stress. An 8-week feeding trial was conducted with experimental diets containing 6.85, 46.90, 88.24, 167.43, 329.21, and 658.69 mg/kg vitamin C (Vc). Some fish were then exposed to acute cooling stress for 24 h and 48 h (transferred from 33℃ water to 27℃ water). The results showed that the serum levels of Complement 3 (C3) in each group after cooling were higher than before cooling, while the levels of serum Complement 4 (C4) showed the opposite pattern. When dietary Vc was 6.85~167.43 mg/kg, the levels of serum immunoglobulin M (IgM) at 24 h and 48 h were higher than at 0 h (P<0.05). However, there were no differences among the treatments with higher dietary Vc supplementation (329.21~658.69 mg/kg; P>0.05). After cute cooling for 48 h, the levels of serum lysozyme (LZM) were lower than at 0 h, but the Vc-supplemented groups were higher than the control group (P<0.05). The concentration of hepatic malondialdehyde (MDA) were higher in all groups after cooling stress than before cooling stress, but decreased with increasing levels of dietary Vc (P<0.05). Total superoxide dismutase (T-SOD) activity initially increased but then decreased with greater cooling time, and the glutathione (GSH) content increased with increasing dietary Vc supplementation. Heme oxygenase-1 (HO-1) activity in the 6.85 mg/kg Vc group was higher after cooling stress, but the groups supplemented with 88.24 to 167.43 mg/kg Vc had lower activities after cooling (P<0.05). The levels of heat shock proteins (HSP70) were higher before acute cooling, and when cooled for 48 h, HSP70 levels in the Vc -supplemented groups were lower than the control group (P<0.05). These results suggest that dietary Vc supplementation (46.90~167.43 mg/kg) may improve antioxidant capacity, reduce lipid peroxidation, and enhance the resistance to acute cooling in L. maculatus.
