Effects of dietary arginine levels on intestinal morphology, digestive enzyme activity, antioxidant capacity and intestinal flora of hybrid snakehead(Channa maculata ? x Channa argus ? )

The effects of arginine on intestinal shape, digestive enzyme activity, antioxidant capacity, and intestinal flora of hybrid snakeheads Channa maculata ? x Channa argus ? . Five experimental diets were formulated to contain arginine with 2.31%, 2.42%, 2.72%, 2.92%, and 3.12% respectively, and recorded as G1 (control), G2, G3, G4, and G5. Five groups of 50 fish (22.02 +/- 0.02 g) for each diet were fed to apparent satiation twice daily for 56 days. The results showed that significantly higher weight gain (WG), specific growth rate (SGR), protein depo-sition rate (PDR), intestinal somatic indices (ISI), lipase, trypsin, Na+/K+-ATPase, gamma-glutamyl transpeptidase, and significantly lower feed coefficient rate (FCR) were observed in fish fed with 2.92% diet compared to 2.31% group (P < 0.05). There was a significant increase of intestinal villus length, villus width and muscular thickness in fish fed with 2.92% and 3.12% arginine diets compared with those in 2.31% group (P < 0.05). The fish fed with 2.92% or 3.12% arginine diets had significantly higher intestinal total antioxidant capacity (T-AOC), catalase (CAT), superoxide dismutase (SOD), peroxidase (POD), glutathione peroxidase (GSH-Px) and lower malondialdehyde (MDA) compared to those in 2.31% group (P < 0.05). High-throughput sequencing revealed arginine supplementation can significantly increase the generation of probiotic bacteria and altered the composition of intestinal microbes. There was a significant increase of the abundance of Firmicutes and Pro-teobacteria in fish fed 3.12% arginine diets compared with those in 2.31% group (P < 0.05). Based on the WGR, a broken-line regression analysis showed that the appropriate level of arginine in the diet of hybrid snakehead was 2.95% (6.65% of the feed protein).