Abstract
A 60-day feeding trial was conducted to determine the effects of different dietary vitamin C levels on growth performance, immune response and antioxidant capacity of loach juveniles. Six isonitrogenous (58.6% of crude protein), isoenergetic (17.5 kJ g−1) practical diets supplemented with 0 (VC0), 100 (VC100), 200 (VC200), 500 (VC500), 1000 (VC1000) and 5000 mg kg−1 (VC5000) of VC (35% ascorbic acid equivalent) were fed to fish (mean initial weight 0.11 ± 0.02 g) in triplicate. Results showed that fish fed VC0 diet had significantly lower body weight gain (BWG) and survival rate (SR). However, BWG and SR improved significantly in fish fed VC100 and VC200 diet respectively. Whole body ascorbic acid concentration increased with incremental dietary VC levels from 0 to 100 mg kg−1. The activity of mucus alkaline phophatase was significantly increased by the dietary VC level. Incremental levels of VC significantly reduced activities of glutathione peroxidase (GPx) and catalase. Moreover, fish fed diets containing more than 100 mg kg−1 VC significantly down-regulated the superoxide dismutase and GPx mRNA expression in liver. Meanwhile, the expressions of liver heat shock protein (HSP70) and nuclear factor-erythroid 2-related-2 (Nrf2) were affected by fish fed diets containing VC from 100 to 5000 mg kg−1. In conclusion, VC requirement of loach juveniles for optimum growth and functionally preventing lipid peroxidation was more than 200 mg kg−1 of diet. Moreover, high dose of VC supplementation did not show any detrimental effects on loach growth performance.
Published Version
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