Fishes exhibit an astounding diversity of locomotor behaviors from classic swimming with their body and fins to jumping, flying, walking, and burrowing. Fishes that use their body and caudal fin (BCF) during undulatory swimming have been traditionally divided into modes based on the length of the propulsive body wave and the ratio of head:tail oscillation amplitude: anguilliform, subcarangiform, carangiform, and thunniform. This classification was first proposed based on key morphological traits, such as body stiffness and elongation, to group fishes based on their expected swimming mechanics. Here, we present a comparative study of 44 diverse species quantifying the kinematics and morphology of BCF-swimming fishes. Our results reveal that most species we studied share similar oscillation amplitude during steady locomotion that can be modeled using a second-degree order polynomial. The length of the propulsive body wave was shorter for species classified as anguilliform and longer for those classified as thunniform, although substantial variability existed both within and among species. Moreover, there was no decrease in head:tail amplitude from the anguilliform to thunniform mode of locomotion as we expected from the traditional classification. While the expected swimming modes correlated with morphological traits, they did not accurately represent the kinematics of BCF locomotion. These results indicate that even fish species differing as substantially in morphology as tuna and eel exhibit statistically similar two-dimensional midline kinematics and point toward unifying locomotor hydrodynamic mechanisms that can serve as the basis for understanding aquatic locomotion and controlling biomimetic aquatic robots.

鱼类表现出惊人的多样化运动行为，从经典的用身体和鳍游泳到跳跃、飞行、行走和挖洞。在波动游泳期间使用身体和尾鳍 (BCF) 的鱼类传统上根据推进体波的长度和头尾振荡幅度的比例分为：鳗鱼形、亚鲶形、鲶形和鲵形。这种分类最初是根据关键的形态特征（例如身体刚度和伸长率）提出的，以根据鱼类的预期游泳力学对鱼类进行分组。在这里，我们对 44 种不同物种进行了比较研究，量化了 BCF 游泳鱼类的运动学和形态。我们的结果表明，我们研究的大多数物种在稳定运动期间具有相似的振荡幅度，可以使用二阶多项式进行建模。尽管物种内部和物种之间存在显着差异，但分类为鳗形的物种的推进体波长度较短，而分类为鲵形的物种的推进体波长度较长。此外，正如我们从传统分类中所预期的那样，头尾振幅从鳗形运动模式到鱼形运动模式没有减少。虽然预期的游泳模式与形态特征相关，但它们并不能准确地代表 BCF 运动的运动学。