Effects of re-enter water on antioxidant, immune, intestinal flora and metabolome of Chinese mitten crab (Eriocheir sinensis) after high temperature air exposure

Both air exposure stress and heat stress can cause stress responses of Eriocheir sinensis and affect its normal life activities. The objective of this research was to investigate the impact of re-enter water treatment on immunoenzyme activity, immune-related gene expression, hemolymph parameters, intestinal microbiota composition, and metabolomic profiles in Eriocheir sinensis after being subjected to high-temperature air exposure. The findings indicated that the re-enter water effectively mitigated the negative impacts of high-temperature air exposure on both antioxidant and immune capacities. Following treatment with high-temperature air, levels of acid phosphatase (ACP), alkaline phosphatase (AKP), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) were significantly elevated compared to their baseline values (P < 0.05), followed by a decline as re-enter water started with recovery to baseline levels detected at 24 h after re-enter water. Additionally, the levels of heat shock proteins HSP90 and HSP70 exhibited a notable rise after being subjected to high-temperature air. Nevertheless, after 24 h of soaking treatment, these levels reverted to values similar to those recorded initially. However, after re-enter water treatment, the changes in intestinal microbial composition and metabolic level caused by high temperature air exposure were not effectively improved. The analysis of intestinal microbiota revealed that the relative abundance of Bacteroidetes in the recovery group was significantly lower compared to the initial group, whereas the relative abundances of Proteobacteria and Firmicutes were found to be higher than those in the initial group. Concurrently, metabolomics analysis indicated a significant increase in palmitic acid metabolism levels within the high-temperature air group (P < 0.05), while glycine content showed a notable decrease (P < 0.05), and the metabolic changes caused by high temperature air exposure was still not fully recovered after re-enter water.