The molecular mechanism under the behavioral and physiological changes of large yellow croaker (Larimichthys crocea) in response to hypoxia

Abstract

The large yellow croaker (Larimichthys crocea) displays pronounced behavioral changes in response to low oxygen environments, including restlessness, constant floating, and increases in respiratory rate and tail beat frequency. However, the underlying molecular mechanisms governing these behavioral and physiological alterations remain unclear. To address this knowledge gap, the present study employed transcriptome analysis to investigate the molecular responses in the large yellow croaker muscle tissue after the fish were exposed to hypoxic treatment. A total of 4553, 1797, 3222, 3148, and 4815 differentially expressed genes (DEGs) were identified at 1 h, 6 h, 9 h, 24 h, and 72 h after hypoxia treatment, respectively. Subsequent analysis utilizing Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichments unveiled a notable up-regulation of genes related to muscular movement-related pathways, specifically the calcium pathway. This up-regulation coincided with an observed increase in the intracellular Ca2+ concentration and Ca2+ transport enzyme activity, suggesting that hypoxia-induced muscle contraction and relaxation occurred by elevating the intracellular Ca2+ concentration within the muscle tissue. Key DEGs associated with the glycolysis and the TCA cycle pathways were also found to be significantly increased in expression, indicating an activation of energy generation pathways in the muscle of hypoxic large yellow croakers. Conversely, genes related to protein synthesis and cell growth were significantly down-regulated, suggesting an inhibition of energy-consuming processes. Additionally, hypoxia was observed to impact various physiological processes such as oxygen transport, vascular control, and apoptosis. These processes may have been mediated by the up-regulation of HIF-1α and its target genes. Consequently, these results offer novel insights into comprehending the molecular basis of the changes in behavior and physiology of large yellow croaker in response to the stress induced by low oxygen levels.