Liver Transcriptome Analysis Revealed the Physiological Response Mechanism of Red-Spotted Grouper (Epinephelus akaara) Under Acute Hypoxic Stress

Epinephelus akaara is one of the aquaculture species with high commercial value in the aquaculture industry in the Asia-Pacific region. However, acute hypoxia is widespread in the intensive farming and live fish transportation of E. akaara, which seriously hinders the rapid development of the E. akaara farming industry. In this study, transcriptome sequencing (RNA-seq) was conducted on the liver tissues of E. akaara after hypoxia (0.6 ± 0.1 mg/L) for 1, 3, 6 and 9 h. Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that key signaling pathways such as IL-17, HIF-1, TNF and PI3K/Akt were significantly enriched in the hypoxia treatment groups (Hy6 and Hy9). Reverse transcription quantitative polymerase chain reaction (RT-qPCR) analyses revealed that genes linked to energy metabolism, immune response and apoptosis changed significantly in the liver and brain at 6 h and 9 h under acute hypoxia. In addition, three metabolism-related enzymes (GLU, LDH and PK) and two immune-related enzymes (ALT and AKP) all changed significantly at 6 h and 9 h, indicating that 6–9 h was the critical period for physiological stress of E. akaara. In conclusion, these results indicate that E. akaara mediated the organism’s tolerance and adaptation to hypoxic stress by regulating energy metabolism, immune response and apoptosis. This study enriches the regulatory mechanism by which E. akaara adapts to acute hypoxia and is conducive to the breeding of hypoxia-tolerant E. akaara strains.