Effects of low temperature air exposure and immersion on antioxidant, immune, intestinal flora and metabolome of Chinese mitten crab (Eriocheir sinensis)

The aim of this study was to investigate the effects of immersion on immune enzyme activity, haemolymph index, intestinal microbiome and metabolome of E. sinensis after low temperature air exposure. The results showed that low temperature air exposure induced stress response, which led to hepatopancreas injury and increased membrane permeability, but this situation was reversible and alleviated after immersion. In addition, after exposure to low temperature air, haemolymph metabolism-related substances such as glucose and total cholesterol were significantly different from the initial value (P < 0.05), and gradually returned to the initial level after immersion. The changes of intestinal flora and hepatopancreas metabolism caused by low temperature air exposure did not fully recover after immersion, and its negative effects did not completely disappear. The sequencing results showed that the species composition and diversity of intestinal microorganisms of Chinese mitten crabs were changed after low temperature air exposure and immersion treatment. The relative abundance of Bacteroidetes and Proteobacteria were increased, while the relative abundance of Firmicutes was decreased (P < 0.05). Metabolomics analysis showed that lysine levels increased significantly, taurocholic acid levels decreased significantly, and amino acid metabolism and lipid metabolism balance were disturbed in hepatopancreas of E. sinensis after exposure to low temperature air and immersion (P < 0.05). This study will provide new insights into the recovery mechanism of water immersion on Chinese mitten crabs after exposure to air.