Effects of dietary folic acid on the growth, digestive enzyme activity, immune response and antioxidant enzyme activity of blunt snout bream (Megalobrama amblycephala) fingerling

This study carried out a 10-week feeding trial to investigate the effects of dietary folic acid on the growth, digestive enzyme activity, immune response and antioxidant enzyme activity of blunt snout bream (Megalobrama amblycephala) fingerlings. For this purpose, six semi-purified diets were formulated to contain graded levels of folic acid (0.0, 0.5, 1.0, 2.0, 5.0, and 10.0 mg/kg diets), and three tanks (300 l/tank) were randomly arranged and assigned to each experimental diet. Blunt snout bream fingerlings (initial weight 27.0 +/- 0.03 g) were fed with the diets to near satiation four times daily. The results showed that final body weight, weight gain rate, specific growth rate and feed efficiency ratio significantly (P < 0.05) increased with an increasing dietary folic acid level of up to 1.0 mg/kg, plateaued at up to 2.0 mg/kg and thereafter reduced. Fish fedwith 1.0-5.0mg/kg dietary folic acid showed a significant rise (P < 0.05) in Fulton condition factor compared to those fed with an un-supplemented diet, while reverse trends were observed in viscerosomatic and hepatosomatic indexes. Serum urea content of the groups fed with 1.0 and 2.0 mg/kg dietary folic acid, and alkaline phosphate activity of the group fed with a 2.0 mg/kg diet were significantly lower than those fed with the control diet. Muscle crude protein content, serum total protein, complement 3, complement 4 and immunoglobulin M contents, and intestinal amylase, lipase, trypsin and chymotrypsin activities were significantly (P < 0.05) enhanced as the dietary folic acid level increased up to 1.0 mg/kg and thereafter plateaued. Malondialdehyde activity in fish fed with 1.0-5.0 mg/kg dietary folic acid was significantly lower than those fedwith un-supplemented diet, while reverse patterns were found in superoxide dismutase and catalase activities (P < 0.05). Based on the broken line-regression analysis of weight gain rate, specific growth rate and hepatosomatic index, the optimum dietary folic acid for blunt snout fingerlings was estimated to be 0.68, 0.68 and 0.82 mg/kg, respectively. Statement of relevance Vitamins are considered as low molecular weight organic compounds that are required in small amounts for the maintenance of metabolism, normal growth and health of fish. Folic acid is a form of water-soluble vitamin B9, which is important in amino acid and nucleotide metabolism, growth and health of most aquatic animals. Blunt snout bream is a Chinese freshwater herbivorous species that has been recognized as a main aquaculture species, with high economic value which is mostly used in the fresh water polyculture system. Because of an increase in consumer demand and the relatively low production costs of this species, its production has rapidly expanded in China with 0.7 Mt in 2012. Nowadays, several nutritional requirements have been reported about this fish including some vitamin requirements. However, no information is available regarding the folic acid requirement of blunt snout bream. Therefore, this study hypothesized that dietary folic acid may improve growth and digestion, immune and antioxidant capacities of blunt snout bream fingerlings. (C) 2015 Published by Elsevier B.V.