The respiratory quotient (RQ) has been used extensively as an index to evaluate metabolic energy expenditure in terrestrial animals including humans. In contrast, RQ use in understanding physiology and nutrition of aquatic ectotherms has been restricted due to technical challenges in measuring total CO₂ in water. With technical advances in measuring total CO₂ in water, RQ in aquatic ectotherms can be accurately determined and is potentially available as a valuable method. Here, we provide a comprehensive review of studies on RQ and metabolic energy substrate use in aquatic ectotherms. Metabolic energy substrate use is evaluated by a reliable stoichiometric bioenergetic approach, based on measuring RQ and nitrogen quotient (NQ) simultaneously. Stoichiometry provides a non-destructive and unequivocal way to quantify the instantaneous oxidation of each major energy substrate (protein, lipid or carbohydrate). This review aims to refine knowledge about bioenergetics of aquatic ectotherms under different conditions including nutritional aspects of sustainable aquaculture. Notably, stoichiometry provides a promising approach to optimize feeds and feeding regimes to realize sustainable aquaculture under differing conditions and with differing feed ingredients. It also provides an approach to consider climate change impacts and physiological adaptation mechanisms for survival and development in farmed environments and natural ecosystems. Stoichiometric bioenergetics knowledge in aquatic ectotherms has relevance to commercial impacts in the face of overfishing and food security, and ecological significance in the face of environmental change scenarios. We suggest expanding the use of stoichiometry in future bioenergetic research in emerging aquaculture species.

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研究水生变温动物代谢能量底物使用的呼吸商和化学计量方法

呼吸商 (RQ) 已被广泛用作评估包括人类在内的陆生动物代谢能量消耗的指标。相比之下，由于测量水中总 CO _{2 的}技术挑战，RQ 在了解水生变温动物的生理学和营养方面的应用受到限制。随着测量总 CO _{2 的}技术进步在水中，水生变温动物的 RQ 可以准确确定，并且可能作为一种有价值的方法使用。在这里，我们对水生变温动物的 RQ 和代谢能量底物使用的研究进行了全面回顾。基于同时测量 RQ 和氮商 (NQ)，通过可靠的化学计量生物能方法评估代谢能底物的使用。化学计量提供了一种非破坏性和明确的方法来量化每种主要能量底物（蛋白质、脂质或碳水化合物）的瞬时氧化。本综述旨在完善有关不同条件下水生变温动物生物能量学的知识，包括可持续水产养殖的营养方面。尤其，化学计量学提供了一种有前景的方法来优化饲料和饲养制度，以在不同条件和不同饲料成分下实现可持续水产养殖。它还提供了一种方法来考虑气候变化影响和养殖环境和自然生态系统中生存和发展的生理适应机制。水生变温动物的化学计量生物能量学知识与面临过度捕捞和粮食安全时的商业影响有关，以及面临环境变化情景时的生态意义。我们建议在未来新兴水产养殖物种的生物能研究中扩大化学计量学的使用。它还提供了一种方法来考虑气候变化影响和养殖环境和自然生态系统中生存和发展的生理适应机制。水生变温动物的化学计量生物能量学知识与面临过度捕捞和粮食安全时的商业影响有关，以及面临环境变化情景时的生态意义。我们建议在未来新兴水产养殖物种的生物能研究中扩大化学计量学的使用。它还提供了一种方法来考虑气候变化影响和养殖环境和自然生态系统中生存和发展的生理适应机制。水生变温动物的化学计量生物能量学知识与面临过度捕捞和粮食安全时的商业影响有关，以及面临环境变化情景时的生态意义。我们建议在未来新兴水产养殖物种的生物能研究中扩大化学计量学的使用。