Integrated Physiological and Transcriptomic Responses in Gill Tissue of Juvenile Trachinotus ovatus Under Nitrite Stress

Nitrite is a common pollutant in aquaculture. However, the physiological and molecular mechanisms of nitrite toxicity on Trachinotus ovatus have not been well known. In current study, we analyzed the biochemical indexes, cellular apoptosis and transcriptomic response of gills from T. ovatus juvenile under nitrite stress (84.84 mg/L). Results showed that the activities of pyruvate kinase (PK), hexokinase (HK), lactate dehydrogenase (LDH), as well as the contents of reactive oxygen species (ROS) and malondialdehyde (MDA) were significantly increased in the gills of T. ovatus juvenile after nitrite stress. Terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) analysis indicated that apoptotic cells were significantly increased when the time elapsed. A total of 3952 (1784 up-regulation and 2168 down-regulation) differentially expressed genes (DEGs) were identified after nitrite stress for 24 h. The significantly enriched DEGs were mapped to KEGG pathways, such as complement and coagulation cascades (ko04610), cytokine-cytokine receptor interaction (ko04060), and extracellular matrix-receptor interaction (ko04512). Furthermore, the expression profiles of ten representative DEGs, including HSP70, MMP13, HMOX, PTGES, Cfi, Lipc, ATP4B, LY-6D, DC-SIGN, and SLC1A3, were investigated in detail. All results demonstrated that nitrite stress disrupted the energy metabolism of the juvenile T. ovatus, which induced excessive ROS production, triggered cell apoptosis, and ultimately compromised the immune capacity. This research provided important insights into the physiological responses of fish to nitrite stress.