Expression of antioxidant and stress-related genes in olive flounder, Paralichthys olivaceus exposed to high temperatures after pre-heating.

The rising sea surface temperatures driven by climate change cause thermal stress, leading to oxidative stress, metabolic disorders, and increased disease susceptibility, thereby impairing the physiological functions of fish. Therefore, understanding the adaptation mechanisms of fish to high temperatures is essential for mitigating the negative impacts of thermal stress on aquaculture productivity and fish health. In this study, Paralichthys olivaceus were subjected to high temperatures following pre-heating to evaluate the advantages of pre-stimulation prior to exposure to the critical temperature. The P. olivaceus were exposed to four groups; Acute (subjected to acute heat shock at 32 °C), AH-S (exposed to acquired heat shock at 28 °C followed by short recovery of 2 h and subsequent heat shock at 32 °C), AH-L (exposed to acquired heat shock at 28 °C followed by long recovery of 2 days and subsequent heat shock at 32 °C) and AH-SL (combined of AH-S and AH-L protocols). In terms of antioxidant response, mRNA expression (caspase 10, thioredoxin (Trx), superoxide dismutase (SOD), peroxiredoxin (Prx), glutathione-S-transferase (GST), and transferrin (TF)) and enzyme activities (SOD, CAT, and GST) were significantly upregulated in P. olivaceus pre-heated prior to high-temperature exposure (AH-S, AH-L, and AH-SL groups). In addition, the stress gene expressions such as heat shock protein 70 (HSP70), HSP60, HSP90, warm-temperature-acclimation-associated 65-kDa protein (Wap65-1), and glucose-regulated protein 78 (GRP78) was significantly upregulated in AH-S, AH-L and AH-SL groups. Pre-heating has been found to be effective in mitigating thermal stress, with the efficacy varying according to the differences in pre-heating methods.