Acute Alkaline Stress Activates Glucose Metabolism for Energy Supply and Induces the Immune Response in the Oriental River Prawn, Macrobrachium nipponense

Using vacant saline-alkali land for aquaculture has the advantages of resource utilization and significant economic and ecological benefits, but there is a need to understand the impact of variable alkalinity on aquacultural species. This study investigated the impact of different alkaline stress conditions (10 and 20 mmol/L) on transcription and changes in intestinal microbial communities in the oriental river prawn, Macrobrachium nipponense, over a 96-h period. Under low alkalinity conditions, pathways related to carbohydrate metabolism were activated, including glycolysis/gluconeogenesis, mannose metabolism, ascorbate and aldarate metabolism, carbohydrate binding, chitinase activity, and lysosome. Such conditions also led to an increase in the number of beneficial intestinal bacteria, such as Proteobacteria, Firmicutes, Actinobacteriota, and Acidobacteriota. However, high-alkaline conditions inhibited the fibroblast growth factor receptor signaling pathway, store-operated calcium channel activity, and MAPK signaling pathway, and significantly increased the number of pathogenic intestinal bacteria, such as Citrobacter. These results suggest that low alkalinity would promote the growth of M. nipponense by activating the glycolysis pathway and increasing the number of beneficial bacteria. By contrast, high alkalinity would inhibit their immune performance by affecting key signal transduction pathways and increasing harmful bacteria in the intestinal tract. Such insights provide a theoretical basis for the subsequent adaptive aquaculture of M. nipponense in saline-alkali areas.