ABSTRACT: Dissolved oxygen (DO) has an important impact on fish survival and reproduction, and is also one of the keys limiting conditions for healthy fish life. Rainbow trout (Oncorhynchus mykiss), an economically significant cold-water fish globally, are highly susceptible to hypoxia stress. However, the physiological changes and molecular mechanisms of rainbow trout under different hypoxic conditions are still unknown. In the present study, we used RNA-seq analysis and measurement of biochemical parameters at different time points (0-, 4-, 8-, 12-, 24 h) under acute (3.0 ± 0.1 mg/L), chronic (4.5 ± 0.1 mg/L) hypoxic stress and reoxygenation (R12-, R24 h) to reveals the physiological changes and molecular mechanism of the hypoxic stress response in rainbow trout. The transcriptome results showed that a total of 424 differentially expressed genes (DEGs) were identified in the CM-vs-Tm12M, CM-vs-Ts12M and Tm12M-vs-Ts12M groups and the genes for FOXO signaling pathway, p53 signaling pathway, Adipocytokine signaling pathway, Autophagy, Glycine, serine and threonine metabolism, etc. were significantly enriched under hypoxic stress, as shown by Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes enrichment analyses (KEGG) and Gene Set Enrichment Analysis (GSEA). Based on DEGS expression trend analysis, the most significant 2 clusters were selected to construct protein-protein interaction (PPI) networks, which resulted in the prediction of ddit4, txnip, slc3a2 and p4ha1 as the hypoxia-induced hub genes in cluster 7. fgg, f7, serpina1 and serpinf2 are the hypoxia-induced hub genes of cluster 3. This study preliminarily elucidated the adaptive mechanism of rainbow trout in response to hypoxic stress and provide a basis for the study of the molecular mechanism of fish adaptation to different hypoxic stresses.
