Abe Takaaki K, Fuke Maho, Fujioka Ko, Noda Takuji, Irino Hiroyuki, Kitadani Yoshikazu, Fukuda Hiromu, Svendsen Morten Bo Søndergaard, Steffensen John Fleng, Kitagawa Takashi
Atmosphere and Ocean Research Institute, The University of Tokyo, Chiba, Japan.
College of Bioresource Science, Nihon University, Fujisawa, Kanagawa, Japan.
Front Physiol. 2025 May 29;16:1512043. doi: 10.3389/fphys.2025.1512043. eCollection 2025.
Pacific bluefin tuna (; PBT) can maintain their body temperature above ambient water (i.e., thermal excess) through high heat production and heat retention. The endothermic ability develops at 20-40 cm fork length ( ), which has been attributed to improved heat retention. Meanwhile, the contribution of heat-production capacity to the development of thermal excess is insufficiently understood. This study aimed to elucidate the ontogenetic pattern of heat production and its contribution to endothermic capacity in juvenile PBT using a heat-budget model (HBM) and swim-tunnel respirometry. The HBM was applied to 2-4 months of biologging data from juveniles (23-50 cm ; 200-4 kg) to estimate heat production rates ( ), revealing that these rates remained high up to approximately 700 g and declined thereafter. Moreover, the comparison of the development of endothermic capacity with the HBM-estimated parameters suggests that in the early juvenile stages, when PBT rapidly develop the thermal excess, the high contributes to the thermal excess. The high in this stage implied the juvenile-specific development of aerobic capacity; therefore, metabolic rate and aerobic capacity-related tissues (red muscle and ventricle) were measured, and the scaling exponents were calculated in this stage (16-28 cm ; 50-420 g). Swim-tunnel respirometry was conducted on juvenile PBT in Japan (August-September 2022 and 2023), and the collected samples were used to measure red muscle and ventricular masses. The scaling exponents of tunas throughout life history are generally in the range of 0.6-0.9, while those for these traits were 1.0 or greater in this size range, supporting the juvenile-specific aerobic capacity development. In conclusion, this study reveals the ontogenetic characteristics of heat production-related traits in PBT and provides new insights into the developmental process of endothermic ability, beyond heat retention capacity.
太平洋蓝鳍金枪鱼（PBT）能够通过大量产热和保持热量，将体温维持在高于周围水温的水平（即热盈余）。这种吸热能力在叉长20 - 40厘米时开始发育，这被认为是由于热量保持能力的提高。与此同时，产热能力对热盈余发育的贡献尚未得到充分了解。本研究旨在利用热收支模型（HBM）和游泳隧道呼吸测定法，阐明幼年PBT产热的个体发育模式及其对吸热能力的贡献。将HBM应用于幼鱼（23 - 50厘米叉长；200 - 4千克）2 - 4个月的生物记录数据，以估计产热率，结果显示这些产热率在约700克体重之前一直保持较高水平，之后开始下降。此外，将吸热能力的发育与HBM估计参数进行比较表明，在幼年早期，当PBT迅速发展热盈余时，高的产热率有助于热盈余的形成。这一阶段的高产热率意味着幼鱼特有的有氧能力发展；因此，对这一阶段（16 - 28厘米叉长；50 - 420克）的代谢率和与有氧能力相关的组织（红色肌肉和心室）进行了测量，并计算了标度指数。在日本对幼年PBT进行了游泳隧道呼吸测定（2022年8月 - 9月和2023年），收集的样本用于测量红色肌肉和心室质量。金枪鱼整个生命史的标度指数一般在0.6 - 0.9范围内，而在这个大小范围内，这些特征的标度指数为1.0或更高，这支持了幼鱼特有的有氧能力发展。总之，本研究揭示了PBT产热相关特征的个体发育特性，并为吸热能力的发育过程提供了新的见解，超越了热量保持能力。
