Response of microbiota and immune function to different hypotonic stress levels in giant freshwater prawn Macrobrachium rosenbergii post-larvae

This study explored the effects of different hypotonic stress levels on antioxidant capacity, microbial composition, and gene expression of Macrobrachium rosenbergii post-larvae. The salinity of the control group was 15 ‰ (S15), and the hypotonic stress groups included three levels of 10 ‰ (S10), 8 ‰ (S8), and 6 ‰ (S6). Different hypotonic stress levels caused oxidative damage in post-larvae, evidenced by decreased superoxide dismutase (SOD) and anti-superoxide anion free radical (ASAFR). They increased malondialdehyde (MDA), nitric oxide (NO), and inducible nitric oxide synthase (iNOS) levels. Microbiological analysis exhibited that different hypotonic stress levels significantly changed microbial composition and diversity. The microbial composition in the water environment where post-larvae living was different from post-larvae. The pathogenic bacteria, including Vibrio and Flavobacterium, were abundant in S6. Transcriptome analysis showed 2, 7967, 297 DEGs, including 1, 3564, 27 up-regulated genes and 1, 4403, 270 down-regulated genes in S10, S8, and S6 groups, respectively. KEGG enrichment results showed that immune and glucose metabolism-related pathways were enriched significantly. Correlation network analysis demonstrated close interactions among antioxidant parameters, microbes, and differentially-expressed genes. In conclusion, hypotonic stress reduced the antioxidant capacity, caused oxidative damage, and altered microbial composition in M. rosenbergii post-larvae. Moreover, when the salinity is below 8 ‰, hypotonic stress impairs the immune system of M. rosenbergii post-larvae.