Growth, health status and gut microbiota of the scalloped spiny lobster (Panulirus homarus) at different salinities

The scalloped spiny lobster (Panulirus homarus) is a valuable species for aquaculture due to its high commercial value. However, limited information is available regarding the effect of environmental parameters on aqua -culture of P. homarus. This study investigated the growth performance, health status and gut microbiota of P. homarus juveniles cultured at salinity 35 (control), 25, and 15 for 4 weeks. Compared to the control, the survival, weight gain, condition factor and haemolymph cell number were significantly reduced in P. homarus at salinity 15, while no significant differences were found in P. homarus at salinity 25. Compared with the control group, the antioxidant indices including total antioxidant capacity, superoxide dismutase and glutathione peroxidase in the 15 and 25 salinity groups were significantly increased, and malondialdehyde increased significantly only at salinity 15. Compared with salinity 35, salinity 15 significantly changed the structure of gut microbiota, increased within-habitat and between-habitat diversity, and increased the abundance of opportu-nistic pathogens Photobacterium and Vibrio. Unsurprisingly, the functions of the gut microbiota were mainly enriched in the metabolism pathway of the KEGG-level 1, and the KEGG-level 2 pathways with an enrichment abundance of >3000 were all in the metabolism pathway. Interestingly, compared with the salinity of 35, the antibiotic synthesis pathway was significantly inhibited, while the pathways related to bacterial life were significantly enhanced in the salinity 15. In conclusion, salinity changes affect growth, antioxidant capacity, and gut microbiota composition of P. homarus, and the effects of large-scale reductions in salinity (e.g., salinity 15) are generally detrimental.