Effects of dietary vitamin C on the growth performance, muscle composition, non-specific immunity, and resistance of juvenile ivory shell (Babylonia areolata) to ammonia

Vitamin C (VC) plays an essential role in the physiological function and normal growth of aquatic animals. However, the effects and requirements of VC on juvenile ivory shell (Babylonia areolata) are still unknown. This study aimed to investigate the effects of VC on growth, muscle composition, non-specific immunity, and resistance to ammonia stress of B. areolata and determine its requirement for VC. Six experimental diets (Diet 1, Diet 2, Diet 3 Diet 4 Diet 5, and Diet 6) with different levels of VC (0, 100, 200, 400, 800, and 1200 mg/kg diet, respectively) were fed to juvenile B. areolate for 3 months. The weight gain rate (WGR) and specific growth rate (SGR) of B. areolata increased in parallel with the VC content, and those of the 800 mg/kg group were significantly higher than those of the control group. There was no significant difference in the survival rate (SR), flesh shell ratio (FSR), viscerosomatic index (VSI), soft tissue index (STI), and muscle composition among the experimental groups. VC (800 mg/kg) significantly increased the total antioxidant capacity (T-AOC) of the hepatopancreas. In addition, VC (400-800 mg/kg) significantly increased the activities of superoxide dismutase (SOD) and alkaline phosphatase (AKP) of the hepatopancreas and significantly decreased the content of malondialdehyde (MDA). VC significantly induced the expression levels of functional genes, such as SOD, GST, CYP450, ferritin, mucin-5AC, and CYC in the hepatopancreas and increased the survival rate of B. areolata under ammonia stress. These results indicate that supplementation with dietary VC could increase the growth, antioxidant capacity, immunity, and resistance against the stress caused by ammonia. The optimal dietary VC requirement for juvenile B. areolata was 400-800 mg/kg of VC.