Transcriptomic Analysis of Liver Tissue in Fat Greenling (Hexagrammos otakii) Exposed to Elevated Ambient Ammonia

Fat greenling (Hexagrammos otakii) is an important aquaculture fish species in northern China. Unfortunately, the increase of nitrogen in water has caused considerable losses for the fat greenling aquaculture industry. Studies on detoxification metabolism and immune responses of fat greenling under ammonia stress have not been carried out. We used high-throughput sequencing to extract RNA from the liver of fat greenling, 48 and 96 hours post-exposure, to water containing 30mg/L NH4Cl. A total of 87,675 high-quality unigenes, with a N50 and mean length of 1523bp and 772bp, were obtained by transcriptome profiling. There were 320 and 272 genes (DEGs) identified in the two sampling times (48 and 96h), containing 132 and 137 significantly up-regulated genes, and 188 and 135 down-regulated genes, respectively. Ten DEGs were randomly selected for validation by quantitative PCR. Further annotation and analysis revealed that the DEGs were enriched in the MAPK-signaling pathway, FOXO-signaling pathway, phosphatidylinositol-signaling pathway, cytokine-cytikine receptor interaction, Hippo-signaling pathway, and neuroactive ligand-receptor interaction. These pathways were mainly related to oxidative stress and immune responses. This research provides a valuable resource to further study of detoxification metabolism and immune responses of fat greenling under ammonia stress.