Effects of dietary vitamin E and Zn on growth performance and metabolism rate of common carp (Cyprinus carpio, Linnaeus 1758) during exposure to chronic hypoxia

Oxygen concentration is known as one of the limiting factors in aquaculture production. The present study aimed to evaluate the effects of vitamin E and zinc (Zn) on the metabolic rate and some growth indices in common carp Cyprinus carpio exposed to chronic low oxygen levels. So, 495 fingerling fish with an average weight of 15.38 ± 1.23 g were randomly selected and divided into two independent groups and fed with diets containing different amounts of vitamin E and Zn for 8 weeks. The vitamin E and Zn (E:Zn) concentrations were 0:0, 60:0, 0:20, 60:20 mg/kg for the control groups (C1-C4) and 0:0, 60:0, 0:20, 60:20, 0:40, 120:0 and 120:40 mg/kg for the treatment groups (T1-T4), respectively. All the physicochemical parameters of water except oxygen were the same for both control and treatment groups. Oxygen concentration for the control and the treatment groups were 8.7 ± 0.43 and 4.1 ± 0.38 mg/L, respectively. Chronic hypoxia led to a significant decrease in growth indices such as final weight and body length (p<0.05). In addition, the level of fish basic metabolic rate and maximum fish metabolic rate, aerobic metabolism scope in chronic hypoxia conditions were significantly lower than the control group (p<0.05). Nevertheless, using dietary supplements in the fish diet led to a significant improvement in the examined parameters in the treatment groups (p<0.05). The results of the present study showed that using food supplements, in addition to improving the metabolic rate of fish under chronic hypoxia condition, lead to an elevated efficiency of feeding and growth, which is directly related to the production efficiency of aquaculture systems.