Integrated Transcriptomic and Metabolomic Analysis Suggests Β-Alanine and Arachidonic Acid Metabolism Are Associated with Salinity Stress Adaptation in Red Tilapia

Salinity is a key environmental factor affecting the survival, growth, and reproduction of fish, and the euryhaline red tilapia (Oreochromis spp.) is an ideal model for investigating salinity adaptation mechanisms in fish. In this study, red tilapia (body weight 139.43 ± 41.74 g) were directly transferred from freshwater (control group, C) to water with a salinity of 15 ± 0.1‰ (experimental group, E) for 96 h of acute stress. Gill histological structure, physiological and biochemical parameters, and transcriptomic and metabolomic profiles were analyzed. The results showed that, compared with the 0 h group (control group), SOD activity was significantly elevated at all time points, GSH-Px activity was significantly elevated at 12-24 h, CAT activity was significantly elevated at 36-96 h, and MDA content was significantly increased at 12-48 h (P < 0.05). In gill tissue, slc15a4 expression first increased significantly, falling below the control level at 96 h, whereas cndp2 expression increased continuously and peaked at 96 h. Transcriptomic analysis identified a total of 1088 differentially expressed genes (339 up-regulated and 749 down-regulated), which were significantly enriched in focal adhesion, ECM-receptor interaction, the PI3K-Akt signaling pathway, glutathione metabolism, and the AMPK signaling pathway. Metabolomic analysis identified 250 differentially accumulated metabolites (135 up-regulated and 115 down-regulated), which were significantly enriched in β-alanine metabolism, ABC transporters and multiple metabolic pathways. Integrated multi-omics analysis further revealed that the differentially expressed genes and metabolites were jointly enriched in 12 pathways, including β-alanine metabolism, ABC transporters, neuroactive ligand-receptor interaction, and glycerophospholipid metabolism. In conclusion, β-alanine and arachidonic acid may be interconnected during salinity adaptation in red tilapia.