Physiological and transcriptomic responses of the gills in Gymnocypris eckloni under acute and chronic hypoxia stress

With the intensification of global warming and environmental pollution, hypoxia is an unavoidable environmental factor in aquatic ecosystems and has multiple adverse effects on fish. Gymnocypris eckloni, a representative species of the Qinghai-Tibetan Plateau, exhibits excellent adaptability to hypoxic environments, however, little is known about the hypoxic adaptation mechanisms of G. eckloni. Herein, effects of acute hypoxia for 12 h (H12S) and chronic hypoxia for different durations (H24S, H96S and H168S) on biochemical parameters and transcriptome of G. eckloni gills were investigated. We found that the gills suffered severe oxidative damage and increased anaerobic glycolysis was observed across all groups, and aerobic glycolysis was elevated in H12S. Inflammatory response, apoptosis and translation process were markedly suppressed, and signal transmission and protein synthesis process were strengthened under acute hypoxia stress. Through STEM and WGCNA, we identified several key hub genes (egln, akt, pdk1, foxo1, pfk, gapdh, gk, bax, casp8, il-8 and il-1β) related to hypoxia from 3608 DEGs, and expression of akt, gk, sdh, gapdh and ldh was significantly upregulated under hypoxia stress, and sod1, cat, bax, casp8 and ccl8 showed an opposite trend. Enrichment analysis revealed that most DEGs were significantly enriched in MAPK signaling pathway, cytokine-cytokine receptor interaction, FoxO signaling pathway, mTOR signaling pathway, glycolysis/gluconeogenesis and apoptosis. The study revealed the differences in the molecular mechanisms of G. eckloni in responding to acute and chronic hypoxia stress, and provided valuable genetic resources for breeding hypoxic-tolerant fish.