The effects of sulfate on the physiology, biochemistry, and intestinal transcriptome of Scylla paramamosain under low-salinity conditions

Abstract

Sulfate, a key component of seawater and sulfate-saline-alkali soil, critically impacts aquatic species' physiology. The aim of this experiment was to investigate the effects of sulfate concentration on the growth, survival, microstructure of gills and hepatopancreas, as well as the intestinal immune response and molecular mechanisms of Scylla paramamosain. The experimental groups were categorized as S1 (0 g/L sulfate, sulfate-free), S2 (1 g/L sulfate, optimal concentration), and S3 (2 g/L sulfate, high sulfate concentration). The results showed that with the increase of sulfate concentration in the experimental water, Survival and weight growth rates initially increased but declined at higher sulfate concentrations (P < 0.05), while molting rates progressively decreased. The intestinal ACP and AKP levels in S2 were significantly higher than those in S1 and S3 (P < 0.05). AST and ALT in the S2 group showed no significant difference from those in the S3 group (P > 0.05) but were significantly lower than those in the S1 group (P < 0.05). Sulfotransferases in the S2 group were significantly lower than those in the S1 and S3 groups (P < 0.05). Short-term (72 h) microscopic observations of the gills and hepatopancreas revealed that the gills in both the S1 and S3 groups exhibited thickening of the gill filaments and rupture of the cuticle layer, while the hepatopancreatic tissue in the S3 group also showed enlargement of intercellular spaces, fracture of the basement membrane, and blurred boundaries. Transcriptome sequencing of the S. paramamosain intestine revealed significant upregulation of sulfotransferases in both S1 and S3 groups. GO annotation of DEGs indicated similar responses of S. paramamosain to sulfate-free and high-sulfate environments, maintaining physiological stability by activating protein processing pathways, enhancing blood-lymph coagulation, and regulating redox balance. KEGG analysis revealed that sulfate-free environments predominantly enriched lipid metabolism and secondary metabolism pathways. While those enriched in high-sulfate environments were mainly related to amino acid metabolism and secondary metabolism. The results indicate that both sulfate-free and high-sulfate concentrations affect the growth, survival, and molting rates of S. paramamosain, as well as inducing immune responses in the intestine. In the short term, they can cause structural changes in the gills and hepatopancreas. The intestinal transcriptome expression shows a similar response pattern, but the metabolic pathways differ. This study provides theoretical support and technical guidance for the cultivation of S. paramamosain under low-salinity conditions with sulfate-type saline-alkali water.