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

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 parts per thousand to 3 parts per thousand 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 < 1), including glutamic acid, valine, glycine, fructose, tagatose, and ribose. KEGG enrichment analysis of differential metabolites identified 57 metabolic pathways, of which 29 were statistically significant (P < 0.05), including glycine, serine, and threonine metabolism, the pentose phosphate pathway, and ABC transporters. These metabolic pathways were mostly the amino acid metabolism pathway, carbohydrate metabolism pathway, metabolism of cofactors and vitamins, nucleotide metabolism, energy, metabolism, membrane, transport and translation. 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. The study provides important information about the osmoregulation of S. paramamosain and even other crustaceans.