Abstract
Nano-additives can improve the absorption and utilization of feed nutrients. In this study, we reported the effects of supplementary nano iron (0, 30, 60, 120, 240 and 480 mg/kg) on intestinal tract function of largemouth bass juveniles. Firstly, 60 mg/kg of supplementary nano iron improved the specific growth rate, and significantly increased the height and width of intestinal villi and intestinal absorption area, and improved the intestinal physical barrier of juvenile largemouth bass. Secondly, the supplementation of low concentration of nano iron can significantly increase the activity of intestinal antioxidant enzymes (CAT and T-SOD), enhance the expression of antioxidant-related genes (SOD1, Nrf-2) and proteins (CAT; P < 0.05), and decrease malondialdehyde (MDA) content. Meanwhile, supplementation with 60 mg/kg of nano iron resulted in the highest survival rate following intraperitoneal injection of Nocardia. However, supplementation of 480 mg/kg would compromise the immune and antioxidant capacity of juvenile largemouth bass. This was evidenced by increased expression of inflammatory and apoptotic genes, significant reduction in the expression of intestinal tight junction genes (ZO-1, Acludin1, Acludin7; P < 0.05), impairment of intestinal physical barriers, and exacerbation of oxidative stress levels in the organism, ultimately resulting in decreased immunity. In conclusion, moderate supplementation of nano iron appears to enhance the intestinal physical barrier, antioxidant capacity, and immune function of juvenile largemouth bass.