Integrated Physiological, Transcriptomic, and Gut Microbial Responses of Chinese Mitten Crab (Eriocheir sinensis) to Acute Salinity Stress

The development of aquaculture in saline waters provides a potential strategy for expanding aquatic food production under conditions of freshwater scarcity. However, the specific mechanisms by which economically valuable crustaceans respond to acute salinity stress remain unclear. Here, we investigated the survival and physiological responses of Chinese mitten crabs (Eriocheir sinensis) following acute exposure to a range of salinity levels (0.2‰, 5‰, 20‰, 25‰, and 30‰). After 48 h of exposure, the survival rates were 100%, 100%, 80%, 56.7%, and 26.7% in the 0.2‰, 5‰, 20‰, 25‰, and 30‰ groups, respectively, with survival decreasing significantly at salinities of 20‰ and above. Acute salinity exposure altered gill enzyme activities and hemolymph physiological parameters, with reduced Na⁺/K⁺-ATPase activity and increased carbonic anhydrase activity, osmolality, and ammonia content under the higher-salinity treatments. To characterize the molecular and microbial responses to extreme salinity exposure, gill transcriptomic and gut microbiome analyses were conducted in the 0.2‰ control group and the 30‰ treatment group. Transcriptomic analysis identified differential expression patterns associated with ion transmembrane transport, acid–base regulation, calcium homeostasis, and chitin-related processes. Gut microbiome analysis showed marked changes in microbial community structure, including the enrichment of Candidatus Hepatoplasma, Marinifilum, and Sulfitobacter and the reduced relative abundance of Candidatus Bacilloplasma and Shewanella in the 30‰ group. Tax4Fun analysis predicted significant differences in several microbial functional categories related to metabolism. These results indicate that acute high-salinity stress disrupts ion regulation and acid–base balance, inhibits key ion-transport enzymes, and alters the intestinal microbial community, accompanied by changes in predicted microbial phenotypes and functional profiles. This multi-omics analysis provides physiological and microbial insights into the acute response of E. sinensis to elevated salinity and may inform the culture and health management of this economically important species in saline waters.