Fuji Takehiro, Sumikawa Hiroaki, Hirata Naoya, Kimori Yoshihiro, Kato Masafumi, Fukue Takashi
Department of Mechanical Engineering, Graduate School of Engineering, Kanazawa Institute of Technology, 3-1 Yatsukaho, Hakusan, Ishikawa, 924-0838, Japan.
Mechanical and Aerospace Engineering, Division of Science and Engineering, Iwate University, 4-3-5 Ueda, Morioka, Iwate, 020-8551, Japan.
Sci Rep. 2025 May 8;15(1):16045. doi: 10.1038/s41598-025-00315-9.
Fish leverage the interaction of multiple fins to improve their swimming ability. Acceleration performance, in particular, is a key aspect of locomotion that directly affects survival through predator evasion and prey capture. Most of these studies have focused on body and caudal fin (BCF) swimmers, which are specialized for high-speed locomotion. In contrast, relatively few studies have examined median and paired fin (MPF) swimmers, and fins' functional roles under different locomotor modes remain insufficiently understood. Therefore, MPF swimmers may employ acceleration strategies distinct from those of BCF swimmers. Understanding the effects of fin interaction on acceleration performance in MPF swimming can contribute to a unified understanding of how such interactions influence swimming performance across fishes with different locomotor modes. A type of MPF swimmer is the balistiform, which uses its dorsal and anal fins as the main propulsion organs. We observed the closing of the caudal fins in Rudarius ercodes in balistiform locomotion during acceleration. We hypothesized that R. ercodes increased their average acceleration (the time taken to reach the experimentally observed velocity) by closing their caudal fins. We performed water tank observations to capture swimming behavior and three-dimensional computational fluid dynamics (3D-CFD) analysis to clarify the impact of caudal fin opening and closing on acceleration capability in balistiform locomotion. For example, parameters such as swimming speed and caudal fin spreading angle were measured in the swimming observations. In contrast, the fluid dynamic analysis computed the vortex structures, propulsive efficiency (the ratio of input energy contributing to thrust), and the cost of transport (the energy required to travel a unit distance). Our analysis showed that closing the caudal fin increased the average acceleration by 30%, increased the cost of transport, and decreased the dimensionless Froude efficiency. We also clarified the role of the caudal fin in MPF locomotion straight-line swimming. Our findings will help us better understand how fin interactions affect fish's swimming ability.
鱼类利用多个鱼鳍的相互作用来提高其游泳能力。特别是加速性能，是运动的一个关键方面，它通过躲避捕食者和捕获猎物直接影响生存。这些研究大多集中在专门进行高速运动的体-尾鳍（BCF）游泳者身上。相比之下，研究中鳍（MPF）游泳者的研究相对较少，并且在不同运动模式下鳍的功能作用仍未得到充分了解。因此，MPF游泳者可能采用与BCF游泳者不同的加速策略。了解鳍的相互作用对MPF游泳中加速性能的影响，有助于统一理解这种相互作用如何影响不同运动模式鱼类的游泳性能。一种MPF游泳者是鲀形目鱼类，它将背鳍和臀鳍作为主要推进器官。我们观察到鲀形目运动加速过程中，长鳍吻鲉的尾鳍会闭合。我们假设长鳍吻鲉通过闭合尾鳍来提高其平均加速度（达到实验观测速度所需的时间）。我们进行了水槽观测以捕捉游泳行为，并进行了三维计算流体动力学（3D - CFD）分析，以阐明尾鳍开合对鲀形目运动中加速能力 的影响。例如，在游泳观测中测量了游泳速度和尾鳍展开角度等参数。相比之下，流体动力学分析计算了涡旋结构、推进效率（输入能量中用于产生推力的比例）和运输成本（行进单位距离所需的能量）。我们的分析表明，闭合尾鳍使平均加速度提高了30% , 增加了运输成本，并降低了无量纲弗劳德效率。我们还阐明了尾鳍在MPF直线游泳运动中的作用。我们的研究结果将帮助我们更好地理解鳍的相互作用如何影响鱼类的游泳能力。
