Abstract Temperature is a critical abiotic factor in aquaculture farming. Serum cortisol, glucose, respiratory frequency, hepatic glycogen, anti-oxidant enzyme activities (superoxide dismutase [SOD], catalase [CAT], and glutathione peroxidase [GPx]), malondialdehyde (MDA) content, and expression of heat shock proteins (hsp70, 90) and apoptosis-related genes (p53, caspase3, bax, bcl2) of turbot were determined at 27 °C under different thermal durations (0, 6, 12, 24, 48, 72, 96 h) to illustrate the underlying physiological response mechanisms. Results showed that cortisol and glucose significantly increased at 27 °C from 0 h to 12 h, and then dramatically decreased from 24 h to 96 h. Respiratory frequency manifested similar results to cortisol. Hepatic glycogen content, GPx and CAT activities gradually decreased in a time-dependent manner under thermal stress. However, SOD activity significantly increased at 6, 12, 24 h and then decreased until the end of thermal stress. Hepatic MDA content significantly increased from 12 h to 96 h. In addition, the apoptosis rate of hepatocyte gradually increased under thermal stress. p53, caspase3 and bcl2 mRNAs were significantly up-regulated under thermal stress within 6 h, and down-regulated from 12 h to 96 h. bax mRNA was significantly up-regulated from 0 h to 6 h, and no significant difference was observed from 6 h to 96 h. Hepatic hsp70 and hsp90 mRNAs were significantly up-regulated from 6 h to 12 h, which was similar to those of serum glucose results. These results indicate that hyperthermal stress elevates respiratory frequency, serum cortisol and glucose contents, promotes hepatic glycogenolysis, impairs hepatic antioxidant capacity and induces hepatocyte apoptosis by p53-bax-bcl2 and the caspase-dependent pathways. These findings expand the current knowledge on thermal tolerance and aid the management of turbot in captivity.

中文翻译：

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幼年大菱鲆（Scophthalmus maximus. L）在高温胁迫下的生理反应

摘要 温度是水产养殖中一个关键的非生物因素。血清皮质醇、葡萄糖、呼吸频率、肝糖原、抗氧化酶活性（超氧化物歧化酶 [SOD]、过氧化氢酶 [CAT] 和谷胱甘肽过氧化物酶 [GPx]）、丙二醛 (MDA) 含量和热休克蛋白 (hsp70) 的表达, 90) 和比目鱼的凋亡相关基因 (p53, caspase3, bax, bcl2) 在 27 °C 下在不同的热持续时间 (0, 6, 12, 24, 48, 72, 96 h) 下测定，以说明潜在的生理反应机制。结果表明，皮质醇和葡萄糖在 27°C 时从 0 小时到 12 小时显着增加，然后从 24 小时到 96 小时急剧下降。呼吸频率表现出与皮质醇相似的结果。肝糖原含量，GPx 和 CAT 活性在热应激下以时间依赖性方式逐渐降低。然而，SOD 活性在 6、12、24 小时显着增加，然后下降，直到热应激结束。肝脏 MDA 含量从 12 小时显着增加到 96 小时。此外，热应激下肝细胞凋亡率逐渐升高。p53、caspase3 和 bcl2 mRNA 在 6 小时内在热应激下显着上调，并从 12 小时到 96 小时下调。bax mRNA从0小时到6小时显着上调，从6小时到96小时没有观察到显着差异。肝脏 hsp70 和 hsp90 mRNAs 从 6 小时到 12 小时显着上调，这与血清葡萄糖结果相似。这些结果表明，高温应激会提高呼吸频率、血清皮质醇和葡萄糖含量，通过 p53-bax-bcl2 和半胱天冬酶依赖性途径促进肝糖原分解，损害肝脏抗氧化能力并诱导肝细胞凋亡。这些发现扩展了目前关于耐热性的知识，并有助于圈养大菱鲆的管理。