Growth performance, hematology, antioxidant capacity, immunity, and intestinal microbiota of spotted knifejaw (Oplegnathus punctatus) reared in recirculating aquaculture system and offshore aquaculture net pen

The land (recirculating aquaculture system, RAS)-sea (offshore aquaculture net pen system, OANPS) relay alternate culture is a new model for fish farming based on seasonal changes. However, the characteristics of fish reared by land-sea relay farming are unclear. In the current study, the growth performance, hematology parameters, antioxidant capacity, immune response, and intestinal microbiota of spotted knifejaw reared in the OANPS and RAS were compared to evaluate the feasibility and potential development of land-sea relay alternate culture. Results showed that spotted knifejaw cultured in the OANPS had remarkably higher body weight gain (BWG), specific growth rate (SGR), and serum growth hormone (GH) content than those in the RAS. The serum superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), lysozyme (LZS), respiratory burst (RB), alternative complement activity (ACH50), total protein (TP), globulin (Glb), and phagocytosis index (PI) of fish reared in the OANPS were significantly higher than those of fish reared in the RAS. No significant differences in intestinal microbiota diversity, richness, or dominant microbiota were observed in both systems. Interestingly, LZS, RB, ACH50, and GSH-Px activities were significantly positively correlated with Enterococcus, while the MDA content was negatively correlated with Enterococcus and uncultured_bacterium_f_Enterobacteriaceae. In conclusion, spotted knifejaw obtain the optimal growth performance, hematology, antioxidant capacity, and immunity under the RAS and OANPS alternate farming. These findings provide guidance for the design and management of land (RAS)-sea (OANPS) relay alternate culture for spotted knifejaws and other fish species in captivity.