Effect of dietary choline level on growth performance, body composition and serum antioxidant activity of juvenile largemouth bass (Micropterus salmoides)

An experiment was conducted to investigate the effects of dietary choline content on growth performance, body composition, and serum antioxidant activity of juvenile largemouth bass, Micropterus salmoides. Graded choline chloride levels of 0 (control group), 700, 1 400, 2 100 and 2 800 mg/kg were supplemented to basal diet to formulate five isonitrogen and isoenergy practical diets containing choline of 2 369.57, 2 716.90, 2 993.49, 3 443.60 and 3 799.05 mg/kg, respectively. Each diet was randomly assigned to triplicate cages of 20 fish with an initial average weight of (20.00±0.10) g for 56 days. The results showed that the weight gain rate (WGR) and specific growth rate (SGR) of the fish first increased and then decreased with the increase of dietary choline chloride, and reached the maximum when the dietary supplementation was 2 100 mg/kg, which were significantly higher than those of the control group. The survival rate (SR), hepatopancreas somatic index (HSI), viscera somatic index (VSI), and condition factor (CF) of the fish were not significantly affected by dietary choline chloride supplementation. When the dietary choline chloride supplementation reached 2 100 mg/kg or above, the lipid contents in muscle and liver of the fish were significantly decreased than those in control. Compared with the control group, the total antioxidant capacity, superoxide dismutase and catalase activities were significantly increased and the content of malondialdehyde in serum was significantly decreased in the groups which were supplemented with 1 400, 2 100 and 2 800 mg/kg choline chloride. The maximum of lysozyme activity and minimum of aspartate aminotransferase activity appeared in the group treated with dietary choline chloride of 2 100 mg/kg, which were significantly different from those of the control group. All these results indicated that the suitable dietary choline chloride supplementation could significantly improve growth performance, reduce liver fat content, and enhance the serum's antioxidant capacity. Regression analysis showed that the recommended amount of choline chloride in the practical diet of juvenile largemouth bass was 2 008.50-2 398.16 mg/kg (the dietary choline content was 3 432.09-3 530.23 mg/kg).