摘要Bacterial pathogens destroy the structural integrity of functional organs in fish,leading to severe challenges in the aquaculture industry.Vitamin D3(VD3)prevents bacterial infections and strengthens immune sys-tem function via vitamin D receptor(VDR).However,the correlation between VD3/VDR and the structural integrity of functional organs remains unclarified.This study aimed to investigate the influence of VD3 supplementation on histological characteristics,apoptosis,and tight junction characteristics in fish intes-tine during pathogen infection.A total of 540 healthy grass carp(257.24±0.63 g)were fed different levels of VD3(15.2,364.3,782.5,1,167.9,1,573.8,and 1,980.1 IU/kg)for 70 d.Subsequently,fish were challenged with Aeromonas hydrophila,a pathogen that causes intestinal inflammation.Our present study demon-strated that optimal supplementation with VD3(1)alleviated intestinal structural damage,and inhibited oxidative damage by reducing levels of oxidative stress biomarkers;(2)attenuated excessive apoptosis-related death receptor and mitochondrial pathway processes in relation to p38 mitogen-activated pro-tein kinase signaling(P＜0.05);(3)enhanced tight junction protein expression by inhibiting myosin light chain kinase signaling(P＜0.05);and(4)elevated VDR isoform expression in fish intestine(P＜0.05).Overall,the results demonstrated that VD3 alleviates oxidative injury,apoptosis,and the destruction of tight junction protein under pathogenic infection,thereby strengthening pathogen defenses in the intestine.This finding supports the rationale for VD3 intervention as an essential practice in sustainable aquaculture.