Metabolic mechanism of the mud crab (Scylla paramamosain) adapting to salinity sudden drop based on GC-MS technology

•This study is the first metabolomics study to identify the key pathways and crucial metabolites for the Scylla paramamosain to adapt to sudden salinity decline.•We identified 1264 metabolites, among which 437 were differentially expressed. These metabolites are mainly amino acids and energy metabolites. Among them, taurine is up-regulated. Compared with other different metabolites, it has the highest VIP value, so it plays a very key role in the osmotic regulation of mud crab.•These results suggest that under a sudden decrease in salinity, S. paramamosain synthesizes a large amount of taurine through taurine and hypotaurine metabolism, which is then transported extracellularly via ABC transporters, thereby regulating extracellular osmotic pressure.•The results of this study show that free amino acids play an important role in adaptation to a sudden decrease in salinity and that energy metabolism involving carbohydrates and organic acids provides the energy supply during adaptation. Salinity impacts the respiratory metabolism, growth, and survival of marine crustaceans. Although the S. paramamosain is a euryhaline species, the sudden drop in salinity often causes individual death. The study aimed to reveal the adaptive mechanism of S. paramamosain in response to a sudden drop from 23‰ to 3‰ in salinity based on GC–MS data. We identified 1264 metabolites, and 437 were differentially expressed. Of them, 71 were up-regulated (FC > 1), including taurine, L-homoserine, aspartic acid, fructose 6-phosphate, glucose 6-phosphate, pyruvic acid, and lactic acid, and 74 were down-regulated (FC