Effects of dietary non-starch polysaccharides level on the growth, intestinal flora and intestinal health of juvenile largemouth bass Micropterus salmoides

A 56-day feeding trial was conducted to evaluate the effects of dietary non-starch polysaccharide (NSPs) inclusion on the growth performance, intestinal flora and intestinal health of juvenile largemouth bass (6.00 ± 0.01 g) in quadruplicate. Seven isoproteic and isolipidic diets (crude protein 47.0%, crude lipid 12.5%) were formulated to contain 0%, 3%, 6%, 9%, 12%, 15% and 18% NSPs (each 100 g contains 32.26 g cellulose, 19.35 g arabinoxylan, 4.52 g β-glucan, 5.16 g mannan and 38.71 g pectin; named N0, N3, N6, N9, N12, N15 and N18), respectively. Weight gain rate, specific growth rate, protein efficiency ratio, protein and lipid deposition rate in the N12, N15 and N18 groups were significantly lower than in the N0 group. Plasma diamine oxidase activity and lipopolysaccharide and endothelin-1 concentration in the N15 and N18 groups were significantly higher than in the N0 group. Intestinal occludin, caludin-1, caludin-4, zonulaoccludens-1, interleukin-10, transforming growth factor-β, nuclear factor E2-related factor 2, B-cell lymphoma-2 (Bcl-2), B-cell lymphoma-xl and Bcl-2-associated athanogene expression levels and intestinal peroxidase, catalase and superoxide dismutase activities in the N15 and N18 groups were significantly lower than in the N0 group, while interleukin-8, interleukin-1β, tumor necrosis factor-α, kelch-like ECH-associated protein 1, caspase3, Bcl-2-assoxicated x protein and Bcl-2-associated death protein genes expression levels showed opposite trends. Moreover, the Shannon, Simpson, Chao and Ace indices and the abundance of Plesiomonas shigelloides, [Clostridium] dakarense and Romboutsia ilealis in the N18 group were significantly lower than in the N0 group, in contrast to the abundance of Paraclostridium bifermentans, Mycoplasma moatsii. Propionate, butyrate, valerate and total short-chain fatty acids (SCFA) contents in digesta of the N6 group were significantly higher than in the N0 group, while acetate, butyrate, valerate, caproate and total SCFA in digesta of the N18 group were significantly lower than in the N0 group. Results suggest that high NSPs diets increased intestinal permeability and abundance of pathogenic microorganisms, induced intestinal inflammation and intestinal epithelial cell apoptosis, but decreased intestinal flora α-diversity and SCFA contents, and ultimately impaired growth performance and intestinal health of juvenile largemouth bass. Conversely, low-dose NSPs inclusion had no negative effect on growth and i