Effects of Different Dietary β-Glucan Levels on Antioxidant Capacity and Immunity, Gut Microbiota and Transcriptome Responses of White Shrimp (Litopenaeus vannamei) under Low Salinity

beta-Glucan could significantly improve the antioxidant capacity of aquatic animals. The effects of different dietary levels (0 (control), 0.05, 0.1, 0.2 or 0.4%) of beta-glucan on the growth, survival, antioxidant capacity, immunity, intestinal microbiota and transcriptional responses of Litopenaeus vannamei under low salinity (<= 3) were investigated. The dietary growth trial lasted 35 days (initial shrimp 0.26 +/- 0.01 g). The results indicated that the growth performance of the 0.1% and 0.2% groups was significantly better than that of the control group. A second-order polynomial regression analysis of growth performance against dietary beta-glucan indicated that the optimal dietary beta-glucan level was 0.2% of dry matter. The digestive enzyme activity of the hepatopancreas was enhanced with increasing beta-glucan levels. The antioxidant and nonspecific immunity capacities of the hepatopancreas were also enhanced in the 0.1% group. The alpha-diversity index analysis of the intestinal microbiota showed that the intestinal microbial richness of L. vannamei increased in the 0.1% group. The relative abundance of Proteobacteria decreased in the 0.1% group compared with the control group. The transcriptome results indicate that the prebiotic mechanisms of beta-glucan include upregulating the expression of nonspecific immune genes and osmoregulation genes and activating KEGG pathways associated with carbohydrate metabolism under low-salinity stress. These results suggested that dietary supplementation with beta-glucan markedly increased growth performance and alleviated the negative effects of low-salinity stress by contributing to the activity of biochemical enzymes and enriching carbohydrate metabolism in L. vannamei.

Automated summary

Beta-glucan was found to significantly enhance the antioxidant capacity of Litopenaeus vannamei. Under low salinity conditions, a dietary level of 0.2% beta-glucan was determined to be optimal, promoting improved growth performance, increased digestive enzyme activity, and enhanced antioxidant and immune capacities. Furthermore, beta-glucan positively influenced the intestinal microbiota and activated relevant metabolic pathways. This study provides practical insights for enhancing disease resistance in aquaculture.