Citrus Aurantium Extract Alleviates Growth Reduction, Oxidative Damage, and Intestinal Inflammation in Chinese Soft-Shelled Turtle (Peodiscus Sinensis) Fed Low Fishmeal Diet

The present study investigated the effects of dietary Citrus aurantium extract (CAE) on growth, immunity, antioxidant capacity, and intestinal health of Chinese soft-shelled turtles (Pelodiscus sinensis) fed low-fishmeal diets. Four experimental diets were formulated: a fishmeal-based control (CON), a low-fishmeal diet (NCON), and NCON supplemented with 0.05% (CAE1) or 0.10% (CAE2) CAE. Compared with NCON, both CAE1 and CAE2 increased weight gain, reduced feed conversion ratio, and improved intestinal villus height and epithelial integrity (P<0.05). Digestive enzyme activities including amylase, lipase, and trypsin were higher in CAE-supplemented groups (P<0.05). Serum ACP, AKP, C3, and C4 levels were elevated, and antioxidant indices (SOD, CAT, GSH, T-AOC) in liver and intestinal increased, with MDA decreased (P<0.05). At the transcriptional level, nrf2, sod, cat, and gpx were upregulated in CAE groups, with gpx higher in CAE1 and sod, cat, gpx higher in CAE2 (P<0.05). Pro-inflammatory cytokines (nf-κb, mapk, tnf-α, il-1β, il-6, il-8, tlr2) were downregulated, while anti-inflammatory genes (il-10, tgf-β, ppar-α) and tight junction proteins (zo-1, claudin-1, occludin) were upregulated (P<0.05). In conclusion, Citrus aurantium extract improved growth, antioxidant status, and intestinal health in turtles under low-fishmeal diets.