ABSTRACT: Saline is a key environmental parameter in aquaculture. Research on acute salinity stress can help farmers determine the optimal salinity level to reduce stress responses in fish larvae, improve survival rates, and increase production efficiencies. It can also aid in the selection or breeding of species suited to environments with specific salinities. However, the molecular mechanisms underlying the negative effects of high salinity on Pseudobagras ussuriensis and the regulatory mechanisms underlying its tolerance remain unclear. In this study, Pseudobagras ussuriensis was exposed to 10 g/L NaCl for 96 h, and the physiological and biochemical changes in the gill and kidney tissues were continuously monitored. Transcriptomic and metabolomic analyses of the gill and kidney tissues were conducted at 24 h to elucidate the molecular adaptation mechanisms to salt stress. A total of 2,554 differentially expressed genes (DEGs) were identified in gill and 1,066 DEGs in the kidney tissue, respectively. Compared with the control group, 826 genes were upregulated and 1,728 were downregulated in the gill tissue under acute salinity stress at 24 h, whereas 508 genes were upregulated and 558 were downregulated in the kidney tissue. These DEGs were involved in oxidative stress, energy metabolism, ion transport, and immune responses. Metabolomic analysis showed that compared to the control group, 85 differential metabolites (DMs) were identified in the gill tissue, with 49 upregulated and 36 downregulated, whereas 433 DMs were identified in the kidney tissue, with 252 upregulated and 181 downregulated. Notably, the levels of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) in the kidney and phosphatidic acid (PA) and PC in the gills were significantly increased, while sphingomyelin (SM) decreased. Integrated analysis of metabolomics and transcriptomics through the KGML network map revealed the downregulation of ALDH, ALDH7A1, AOX, and HADHA in the gill, and ENPP1_3, CD203, L-glutamine (downregulated), and Succinic Acid (upregulated) in the kidney. This study combined metabolomics, transcriptomics, and physiological-biochemical analyses to provide new insights into the molecular mechanisms of oxidative stress, energy metabolism, and immune regulation in gill and kidney tissues under acute salinity stress.
