Dietary β‐sitosterol supplementation enhanced intestinal immune function of large yellow croaker ( Larimichthys crocea ) infected with Aeromonas hydrophila

An 80-day feeding trial was performed to investigate the effect of dietary β-sitosterol supplementation on intestinal immune function in large yellow croaker. 540 fish (initial average weight: 189.74 ± 0.31 g) were fed six diets containing graded levels of β-sitosterol (0.0%, 0.5%, 1.0%, 1.5%, 2.0% and 2.5%) and then challenged with Aeromonas hydrophila for 10 days. Results demonstrated that dietary β-sitosterol (1) improved growth performance, attenuated enteritis morbidity and intestinal histopathological lesions; (2) increased lysozyme and acid phosphatase activities, complement 3 and complement 4 contents as well as IgM contents (not in the proximal intestine [PI]) and up-regulated LEAP-2C (rather than LEAP-2A) and hepcidin mRNA expressions in the intestine; (3) down-regulated pro-inflammatory cytokines IL-1β (not in PI), IL-2, IL-6, IL-8, IFN-γ and IFITM mRNA expressions partly associating with NF-κB signalling and up-regulated anti-inflammatory cytokines IL-4/13A (not IL-4/13B), IL-11 and TGF-β mRNA expressions partly associating with TOR signalling in the intestine. Finally, based on percentage weight gain, enteritis morbidity and lysozyme activities in three intestinal segments, the optimal dietary β-sitosterol supplementation levels were estimated to be 1.44%, 2.03%, 2.11%, 1.94% and 1.69% diets respectively. In summary, the optimal dietary β-sitosterol supplementation improved immune function in the intestine of large yellow croaker.