Dietary Fermented Chicory Root Waste Modulates Growth, Chemical Composition, Lipid Metabolism, and Intestinal Barrier Pathways in Common Carp ( <i>Cyprinus carpio</i> L.) Fed With High‐Fat Diets

The current trial sought to assess the impact of fermented chicory root waste (FCRW) dietary administration on growth, lipid metabolism, chemical composition, and intestinal barrier pathway in common carp (<i>Cyprinus carpio</i> L.). Firstly, a single-factor experiment followed by an orthogonal test indicated the optimum factors, such as 30°C for 36 h, a 10% inoculation amount, and a 65% solid-liquid ratio for producing FCRW containing a 12.24% protein. A total of 180 common carp, with an average initial weight of 26.99 ± 4.04 g, were randomly allocated into 12 tanks, with each tank housing 15 individuals. The initial group functioned as the control group (CG) and was provided with a basal diet; meanwhile, the remaining three groups were fed high-fat (HF) diets supplemented with various levels of FCRW, 0%, 5%, and 15% for HF, HF-L, and HF-H, respectively. The feeding trial was prolonged to 56 days. The results of the feeding trial demonstrated that the fish group receiving an HF diet supplemented with a greater proportion of FCRW (15%) exhibited superior growth and feed efficiency. Both 5% and 15% FCRW significantly reduced VSI and HSI, while 15% FCRW increased whole-body crude protein and decreased body/liver lipids. FCRW supplementation also lowered serum/liver triglycerides and serum LDL-C. Additionally, all FCRW levels enhanced antioxidant markers (MDA, AKP, CAT, superoxide dismutase [SOD]) and innate immunity (LZM). Histology showed reduced hepatocyte vacuolation and lipid droplets. Crucially, 15% FCRW upregulated lipolysis genes (<i>lpl</i>, <i>hsl</i>, <i>ppar-α</i>) and downregulated lipogenesis genes (<i>acc-α</i>, <i>fas</i>, <i>ppar-γ</i>). Regarding intestinal structural integrity, FCRW improved intestinal morphology and upregulated barrier genes (<i>occludin</i>, <i>claudin-3</i>, <i>zo-1</i>). It suppressed proinflammatory cytokines (<i>il-1β</i>, <i>il-6</i>) and activated anti-inflammatory pathways (<i>il-10</i>, <i>tgf-β</i>, <i>tlr4</i>, <i>nf-κb</i>). Gut microbiota analysis revealed increased beneficial bacteria (e.g., <i>Firmicutes</i>).