Growth and intestinal health of the red claw crayfish, Cherax quadricarinatus, reared under different salinities

The purpose of this work was to examine immune regulation and the gut microbiota in the red claw crayfish, Cherax quadricarinatus, raised at four different salinities. Juvenile C. quadricarinatus (18.28 ± 0.03 g) individuals were exposed to four salinity levels 0, 5, 10 and 15 practical salinity units (psu) for 35 days. No significant differences in weight gain, specific growth rate, feed conversion ratio or survival were found among the animals in the four treatment groups, but a significantly higher condition factor was obtained in crayfish raised in water with a salinity of 5 psu than in control crayfish. The superoxide dismutase activity of crayfish reared in water at 5, 10 or 15 psu was significantly higher than that of control crayfish. Catalase activity and total glutathione concentrations were significantly higher in crayfish raised at salinities of 10 and 15 psu than in control crayfish. ProPO gene expression levels decreased significantly in the crayfish in the 5, 10 and 15 psu groups. Toll gene expression levels decreased significantly in the crayfish in the 5 psu and 10 psu groups but increased in crayfish in the 15 psu group compared with the control crayfish. Bacteria of the phylum Tenericutes and bacteria of the genus Candidatus_Bacilloplasma were significantly more abundant in the 5, 10 and 15 psu groups, while the abundance of bacteria in the phylum Firmicutes decreased markedly compared with that in the control. The 5 psu group displayed significantly higher values of the Chao1 and ACE richness estimators than the control group. Microbe-mediated functions predicted by PICRUSt showed that 76.94% of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, including environmental information and metabolism, significantly increased in the crayfish in the 5, 10 and 15 psu groups. Taken together, the findings of this study provide guidance for the practical rearing of C. quadricarinatus in brackish water or seawater and contribute to research on stress physiology.