Characterizing transcriptome changes in gill tissue of turbot (Scophthalmus maximus) for waterless preservation

The combined method with high oxygen filling under low temperature and waterless condition is suggested to be a more effective strategy to keep fish alive during turbot transportation. To investigate the biological mechanism of turbot, when turbot was subjected to waterless treatment under different oxygen conditions (water, air and oxygen), the global expression profiling of the gill tissues was performed by transcriptome analysis using Illumina HiSeq 4000 platform. The results showed that a total of 104,886 unigenes were detected, and differential expression analysis revealed 662 differentially expressed genes (322 upregulated (fold > 2) and 340 downregulated (fold < 0.5)) in the Air-group, and 244 up-regulated and 197 down-regulated genes in the Oxygen-group in comparison with the control (in water at 2 degrees C), and 354 up-regulated and 212 down-regulated genes in the Oxygen-group compared to the Air-group were identified. In addition, the reliability of the sequencing results was confirmed using qPCR, the fold change of 6 randomly selected genes were consistent with the results of the sequencing. Moreover, gene ontology analysis was conducted, which indicated that the air environment with waterless has a greater impact on the metabolism of fish compared with the water environment. It was supposed that turbot may regulate their metabolism by increasing the expression of genes involved in transcription and promoting the oxidative stress response in order to maintain homoeostasis. Furthermore, GO and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis showed that the differentially expressed genes were enriched in lyase activity, immune response, cytokine activity and nitrogen metabolism, revealing that oxygen availability influences above metabolic activities in response to waterless conditions. This study provides a novel insight into the mechanism of physiological changes of turbot during waterless transportation.