Transcriptome Analyses Reveal the Molecular Response of Juvenile Greater Amberjack (Seriola dumerili) to Marine Heatwaves

Marine heatwaves (MHWs) have recently become more frequent, intense, and prolonged, posing significant threats to marine life and fisheries. In this study, transcriptomic analysis was employed to investigate the genes and pathways in <i>Seriola dumerili</i> that respond to MHW-induced stress at 28 °C (T28) and 32 °C (T32), using 24 °C (T24) as the control. Transcriptome sequencing revealed that 17 differentially expressed genes (DEGs) belonging to the heat shock protein (HSP) families-HSP30, HSP40, HSP70, and HSP90-were significantly upregulated under short-lasting MHW stress in the T24-4d vs. T32-4d comparison. Additionally, genes related to oxidative stress (e.g., protein disulfide isomerase family A member 6 [<i>pdia6</i>]), immune responses (e.g., interferon regulatory factor 5 [<i>irf5</i>]), and energy metabolism (e.g., hexokinase-1 [<i>hk1</i>]) were also identified. Enrichment analysis of DEGs in the T24-4d vs. T32-4d group revealed that <i>S. dumerili</i> exhibited adaptive responses to MHWs through the upregulation of HSPs and the activation of antioxidant, energy metabolism, and immune response pathways. However, in the T24-13d vs. T32-13d group, DEGs associated with these pathways were either not significantly expressed or were downregulated. These findings indicate that <i>S. dumerili</i> is unable to sustain its adaptive responses under repeated, intense MHW exposure, resulting in the disorder of its antioxidant defense system, immune suppression, and metabolic dysfunction. This study provides valuable insights into the molecular responses of <i>S. dumerili</i> to MHWs and supports the selection for thermal resistance in this species.