Salinity affects the lipid metabolism and intestinal microbial composition of swimming crab Portunus trituberculatus

The swimming crab ( Portunus trituberculatus ) is an aquaculture species with high commercial value. However, there is limited information available on the effects of salinity on the lipid metabolism and gut microbiota of P. trituberculatus . This study investigated the hepatopancreatic index, hepatopancreatic lipid metabolism, physiological and biochemical indicators and gut microbiota of P. trituberculatus cultured at salinity 28 ‰, 25 ‰, 22 ‰ and 19 ‰ for 8 weeks. The results showed that the highest expression level of SREBP1, FAS , LPR1 , ACOX and FABP was found in 19 ‰ group compared to the 28 ‰ group, along with the enzyme activities of CPT1 and FAS. On the contrary, the expression level of DGAT1 and LPR2 in the 28 ‰ group was significantly higher than that of 19 ‰ group, along with the enzyme activities of LPS. The results of fatty acid content showed that only polyunsaturated fatty acids showed significant changes in response to salinity, such as C18:2n6, C20:2n6 and C20:3n3. Moreover, the intestine microbial α-diversity index of crab in the 28 ‰ treatment was higher than that of other groups. The dominant phylum in gut samples was Proteobacteria , followed by Firmicutes and Bacteroidota . Moreover, Mycoplasma , Candidatus Endoecteinascidia and Shewanella showed a significant decline in the 28 ‰ group compared to the 19 ‰ group. Bacterial functional pathway prediction has also shown that the KEGG pathways involved in ovarian steroidogenesis, NF-kappa B signaling pathway and regulation of lipolysis in adipocytes increased in 28 ‰ group compared with 19 ‰ group. In conclusion, hepatopancreatic fatty acid metabolism was more active in the 19 ‰ group, whereas the 28 ‰ group not only promoted triglyceride synthesis in the hepatopancreas, but also facilitated ovarian development of P. trituberculatus by influencing the gut microbial composition. • Highest expression level of SREBP1, FAS, LPR1, ACOX and FABP was found in 19 ‰ salinity treatment. • The intestine microbial α-diversity index in 28 ‰ treatment group was higher than that of other treatment groups. • Ovarian steroidogenesis and regulation of lipolysis in adipocytes pathways were upregulated in 28 ‰ group.