| Summary: | Four diets containing different carbohydrate-to-protein ratios including the control (18% carbohydrate, 45.98% protein), 0.51 C/P (22% carbohydrate, 43.55% protein), 0.58 C/P (24% carbohydrate, 42.33% protein) and 0.72 C/P (28% carbohydrate, 38.91% protein) were designed to investigate the effects of dietary carbohydrate-to-protein ratios (C/P) on the growth performance, antioxidant capacity and energy metabolism in Marsupenaeus japonicus. Totals of 300 shrimp with an average initial weight of 1.08 ± 0.01 g were randomly assigned to four different dietary treatments. Each treatment included three 300 L tanks, with 25 shrimp in each tank. The results indicated that although growth performance had a decreased trend with increased carbohydrate-to-protein ratios, no overall difference (P > 0.05) was observed. There was a significant decreased trend (P < 0.05) in the acitivity of serum superoxide dismutase (SOD) and glutathione peroxidase (GSH) with the increased carbohydrate-to-protein ratios. It’s worthy noting that inter-tissue differences existed in the antioxidant capacity of M.japonicus in response to dietary different carbohydrate-to-protein ratios. The expression of the antioxidant genes (superoxide dismutase isoform 5, sod-5; peroxiredoxin, prx; ferriten) and heat shock protein 70 in intestine was up-regulated (approximately 20–250 fold) (P < 0.05), while the expression of antioxidant genes (sod-5, prx, ferriten) in hepatopancreas was lowered (P < 0.05) with the dietary increased carbohydrate-to-protein ratios. With the dietary increased carbohydrate-to-protein ratios, energy metabolism genes were up-regulated (P < 0.05) while the pepck1 level was down-regulated (P < 0.05) in the hepatopancreas. In addition, there was a first increased and then decreased trend (P < 0.05) of energy metabolism associated gene expressions in intestine. When shrimp fed with 0.72 C/P diet, although above energy metabolism associated genes expression except pepck1 showed a downward trend, its value was still significantly higher (P < 0.05) compared with the control group. In conclusion, although growth performance was not significantly influenced by different carbohydrate-to-protein ratios, antioxidant capacity and energy metabolism was affected in M.japonicus. The response mechanism to different carbohydrate-to-protein ratios showed tissue-specific. Hepatopancreas and intestine were collaborative to regulate antioxidant and energy metabolism in M.japonicus.
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