Transcriptomic responses of the liver of mandarin fish (Siniperca chuatsi) under hypoxic stress

Environmental hypoxia is becoming more prevalent in aquatic environments of mandarin fish (Siniperca chuatsi) aquaculture because of eutrophication and climate change. Little information is available on the molecular mechanisms of the detrimental effects of hypoxia in this species. In this study, the authors assembled a transcriptome for mandarin fish exposed to lower oxygen conditions at different times (24 and 96 h). The antioxidant enzymatic activities of catalase, glutathione, superoxide dismutase, glutamic pyruvic transaminase and malondialdehyde significantly increased at 6 or 12 h but decreased after reaching a climax during 96 h hypoxia stress. The gene ontology study revealed 27,616 transcripts, whereas the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed 25 linked pathways. Significant changes in the expression of certain genes involved in protein processing in the endoplasmic reticulum, the calcium signalling system and inositol phosphate metabolism were discovered using the KEGG pathway analysis. In the liver, 97 genes were differentially expressed between the control and experimental groups. The expression level of 28 differentially expressed genes (DEGs) under different hypoxic stress conditions was detected using real-time PCR and compared to transcriptome sequencing results. The result showed that some genes in the experimental group associated with hypoxic stress, such as hif, ho-1a, ho-1b, igfbp1, hsp90 alpha and hsp90 beta, were significantly upregulated compared with those in the control group. The large amount of transcriptome data from this research has enlarged the mandarin fish gene and genome bioinformation. The identified DEGs and pathways are useful in further studies of biological responses to hypoxia.