Weber Allison V, Craig Paul M
Department of Biology, University of Waterloo, 200 University Ave West, Waterloo, ON N2L 3G1, Canada.
Conserv Physiol. 2025 Apr 15;13(1):coaf027. doi: 10.1093/conphys/coaf027. eCollection 2025.
Understanding metabolic responses to temperature elevations is critical for determining how fish populations will be impacted by the increased occurrence of extreme heat events. Here, we characterized the thermal tolerance limits and metabolic functions of three closely related darter species native to the Grand River of Southern Ontario: Fantail darter e; FTD), Rainbow darter ( RBD) and Johnny darter ( JD). Brain and heart activity of enzymes associated with cellular respiration were analysed for each species at 15°C baseline and following a Critical Thermal Maximum (CT) test. Additionally, aerobic scope (AS) was determined for each species while exposed to four heat ramps designed to mimic previously recorded heatwaves. CT significantly differed between species with FTD displaying the highest at 33.3°C, JD second at 31.8°C and RBD the lowest at 30.7°C. In darters not exposed to heat stress, FTD possessed higher brain enzymatic activity rates, specifically in pyruvate kinase (PK), citrate synthase (CS) and malate dehydrogenase (MDH). These patterns shifted slightly after exposure to CT, with JD displaying a substantial elevation in PK, lactate dehydrogenase, CS and MDH activity, suggesting they had greater enzymatic capacity at temperature extremes. Within heart tissue, we observed no interspecific differences at baseline temperatures; however, RBD had lower enzyme activity than FTD or JD in all enzymes but cytochrome c oxidase following CT. Metabolically, FTD exhibited the highest AS following exposure to 10 and 15°C temperature elevations. Our findings demonstrate that FTD may be the best equipped to respond to temperature-induced increases in metabolic demand due to their elevated baseline enzymatic activity and broader AS. These insights may contribute to future darter conservation efforts by informing predictions on species population shifts, particularly in the context of climate change.
了解鱼类对温度升高的代谢反应对于确定极端高温事件增加将如何影响鱼类种群至关重要。在此，我们描述了安大略省南部格兰德河原产的三种密切相关的镖鲈物种的热耐受极限和代谢功能：扇尾镖鲈（FTD）、虹镖鲈（RBD）和乔氏镖鲈（JD）。在15°C基线温度下以及进行临界热最大值（CT）测试后，对每个物种与细胞呼吸相关的酶的脑和心脏活性进行了分析。此外，在每个物种暴露于四个旨在模拟先前记录的热浪的热梯度下时，测定了有氧代谢范围（AS）。不同物种之间的CT存在显著差异，FTD的CT最高，为33.3°C，JD其次，为31.8°C，RBD最低，为30.7°C。在未受热应激的镖鲈中，FTD具有较高的脑酶活性率，特别是丙酮酸激酶（PK）、柠檬酸合酶（CS）和苹果酸脱氢酶（MDH）。暴露于CT后，这些模式略有变化，JD的PK、乳酸脱氢酶、CS和MDH活性大幅升高，表明它们在极端温度下具有更大的酶能力。在心脏组织中，我们在基线温度下未观察到种间差异；然而，在CT后，除细胞色素c氧化酶外，RBD在所有酶中的酶活性均低于FTD或JD。在代谢方面，暴露于温度升高10°C和15°C后，FTD表现出最高的AS。我们的研究结果表明，由于FTD的基线酶活性较高且AS较宽，它们可能最有能力应对温度诱导的代谢需求增加。这些见解可能有助于未来镖鲈的保护工作，为物种种群变化的预测提供信息，特别是在气候变化的背景下。
