Dietary -Glucan Alleviates Antibiotic-Associated Side Effects by Increasing the Levels of Antioxidant Enzyme Activities and Modifying Intestinal Microbiota in Pacific White Shrimp (Litopenaeus vannamei)

Antibiotics and their secondary metabolites are commonly found in aquatic ecosystems, leading to the passive exposure of many aquatic animals to low doses of antibiotics, which can affect their health. However, there is limited information available on how to mitigate the side effects of antibiotics on normal aquatic animals. This study aimed to investigate the potential of dietary beta-glucan to alleviate the side effects induced by antibiotics in Pacific white shrimp (Litopenaeus vannamei) (0.37 +/- 0.02 g). A six-week feeding trial was conducted with four dietary treatments including a control, 1 g/kg beta-glucan (beta-glucan), 50 mg/kg oxytetracycline (OTC), and a combination of 50 mg/kg OTC and 1 g/kg beta-glucan (Mix) groups. At the end of the trial, the growth performance, intestinal microbial composition, antioxidant capacity, and immune response of the shrimp were assessed. There were no significant differences in growth performance among the groups, but the condition factor of the shrimp in the Mix group was significantly decreased when compared to the control and beta-glucan groups. The activities of hepatopancreas catalase (CAT) and serum phenol oxidase in the OTC group were significantly lower than those in the control group. On the other hand, the activities of hepatopancreas superoxide dismutase and CAT enzymes in the beta-glucan group were significantly higher than those in the OTC group. The supplementation of beta-glucan in combination with antibiotics significantly increased the CAT activity and bacteriolytic activity compared to the OTC and control groups, respectively. Moreover, an analysis of the intestinal microbiota revealed that the Observed_species estimator in the Mix group was significantly higher than that in the control group. Dietary antibiotics significantly increased the abundance of Actinobacteria at the phylum level, but the Mix group showed no significant difference. The supplementation of beta-glucan in combination with antibiotics also significantly increased the relative abundance of Meridianimaribacter compared to the control group. Additionally, the synergistic influence of beta-glucan with antibiotics increased the beta diversity of intestinal microbiotas. These findings suggest that the supplementation of beta-glucan in combination with antibiotics on Pacific white shrimp can alleviate the low antioxidant capacity and immune response caused by antibiotics while enhancing the intestinal microbial composition. This provides a potential solution to mitigate the negative impacts of antibiotics in aquaculture.