Emerging role of vitamin D in alleviating intestinal structure injury caused by in grass carp ().

Bacterial pathogens destroy the structural integrity of functional organs in fish, leading to severe challenges in the aquaculture industry. Vitamin D (VD) prevents bacterial infections and strengthens immune system function via vitamin D receptor (VDR). However, the correlation between VD/VDR and the structural integrity of functional organs remains unclarified. This study aimed to investigate the influence of VD supplementation on histological characteristics, apoptosis, and tight junction characteristics in fish intestine during pathogen infection. A total of 540 healthy grass carp (257.24 ± 0.63 g) were fed different levels of VD (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 , a pathogen that causes intestinal inflammation. Our present study demonstrated that optimal supplementation with VD (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 protein kinase signaling ( < 0.05); (3) enhanced tight junction protein expression by inhibiting myosin light chain kinase signaling ( < 0.05); and (4) elevated VDR isoform expression in fish intestine ( < 0.05). Overall, the results demonstrated that VD 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 VD intervention as an essential practice in sustainable aquaculture.