Enhancing shrimp growth and immunity with green algal Caulerpa lentillifera polysaccharides through gut microbiota regulation

The polysaccharides from green algal Caulerpa lentillifera (CLP) have shown strong positive effects on terrestrial animal immunity. However, little is known about their function in aquatic animals. Here, we fed shrimp with diets containing different CLP contents (0, 0.1 %, 0.2 %, and 0.4 %). Our results indicated that the increase of 0.1 % CLP could significantly enhance shrimp growth rate, weight gain, and hepatopancreas index, and all doses of CLP could greatly increase the shrimp crude protein content compared to the control. In addition, 0.1 % CLP significantly enhanced the shrimp phagocytic activity, hepatopancreatic acid phosphatase (ACP) activity, hepatopancreatic alkaline phosphatase (AKP) activity, and plasma superoxide dismutase (SOD) activity, while reducing plasma malondialdehyde (MDA) activity compared to the controlled diet. The 16S rDNA sequence of shrimp intestine microbiota indicated that the intestinal microbiota diversity in shrimp fed with 0.2 % CLP diets was higher than that in the control, including an increase in beneficial microbial groups (Proteobacteria, Actinobacteria, Firmicutes, and TM7) and a decrease in harmful ones (Shewanella and Vibrio). Feeding with CLP could enrich carbohydrate and amino acid metabolism. Correlation analysis indicated that peroxidase (POD) had the widest correlation with communities, being inversely correlated with seven distinct microbial taxa. Moreover, four distinct microbial taxa were significantly associated with weight. These data indicate that CLP is a potential shrimp forage supplement and recommend the optimum dose of CLP inclusion to be 0.1 %–0.2 % in shrimp diets.