Carbonate saline-alkali water has significant potential in the development of saline-alkali fisheries, but the effects of bicarbonate stress on crustaceans have not been fully studied. In this study, we investigated the changes in osmotic regulation, immune, and antioxidant capacity of the Scylla paramamosain at 1, 7, and 28 d at different carbonate concentrations (CK: 220 mg/L; AB1: 300 mg/L; AB2: 380 mg/L; AB3: 700 mg/L), and conducted transcriptome analysis. The results showed that Ca2+/Mg2+-ATPase in the gills of the AB3 group was significantly lower than that of the AB2 group, while the AB2 group was lower than the CK group and the AB1 group (P<0.05). CA activity was positively correlated with bicarbonate concentration, while the AB3 group was significantly higher than the other groups. ALT and AST in groups AB1 and AB2 showed a trend of first increasing and then decreasing, and roughly returned to their initial levels at 28 d, while AB3 continued to increase with time and was significantly higher than the initial level. At 28 d, ACP and AKP in the AB3 group were significantly lower than those in the other groups. The MDA content in the hepatopancreas also showed similar trend, with a positive correlation between the T-AOC, GSH and bicarbonate concentration. At 28 d, the AB1 group was able to recover to its initial level, while the AB3 group decreased with time and reached its minimum value at 28 d. Transcriptomic analysis identified 283 DEGs, and KEGG enrichment analysis showed antioxidant pathways, including the ascendate and alderate metabolism, were up-regulated to cope with stress. In addition, it shows many immune related pathways, including the mTOR signaling pathway, were significantly down-regulated. This study explores the effects of bicarbonate stress on the S. paramamosain, providing theoretical guidance for the utilization of carbonate saline-alkali water.
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