D'AoUT K, Aerts P
Department of Biology, University of Antwerp (U.I.A.), Universiteitsplein 1, B-2610 Antwerpen, Belgium.
J Exp Biol. 1999 Jun;202 (Pt 11):1511-21. doi: 10.1242/jeb.202.11.1511.
In addition to forward undulatory swimming, eels (and some other elongated swimmers) can swim backwards in a similar way. We compared the kinematics (wave speed, cycle frequency, amplitude, local bending and estimated muscle strain) of forward and backward swimming in the European eel Anguilla anguilla. Both swimming modes are characterised by a wave of undulation that travels over the body in the direction opposite to that of swimming. We observe two major kinematic differences. First, the slope of wave frequency against swimming speed is significantly higher for backward than for forward swimming. Second, the amplitude profile along the body of the propulsive wave differs greatly. During forward swimming, the yaw at the head is minimal and the amplitude of the propulsive wave increases to approximately 15 % (left-to-right) of total body length towards the tail tip. During backward swimming, the amplitude profile is rather uniform along the body (with values similar to the tail-tip amplitude during forward swimming), resulting in considerable lateral head oscillation. Strikingly, the head remains approximately parallel to the swimming direction, which presumably enhances visual and acoustico-lateral perception. Furthermore, muscle strain is much higher in the rostral part of the body during backward swimming than during forward swimming. Values for stride length and propeller efficiency suggest that backward undulatory swimming is mechanically less efficient than forward swimming. We suggest that the typical anguilliform body shape is an important feature that allows these animals to swim backwards using an undulatory mechanism that resembles the forward undulatory swimming mechanism. Most other fishes, if able to swim backwards at all, do so using fin oscillations or undulations.
除了向前的波动式游动外，鳗鱼（以及其他一些细长的游泳者）也能以类似的方式向后游动。我们比较了欧洲鳗鲡（Anguilla anguilla）向前和向后游动的运动学特征（波速、周期频率、振幅、局部弯曲和估计的肌肉应变）。两种游动模式的特点都是有一波波动沿着身体向与游动方向相反的方向传播。我们观察到两个主要的运动学差异。第一，向后游动时波频率相对于游动速度的斜率明显高于向前游动时。第二，推进波沿身体的振幅分布有很大不同。向前游动时，头部的偏航最小，推进波的振幅朝着尾尖增加到大约全身长度的15%（从左到右）。向后游动时，振幅分布沿身体相当均匀（值与向前游动时尾尖的振幅相似），导致头部有相当大的侧向摆动。引人注目的是，头部大致保持与游动方向平行，这大概增强了视觉和听觉侧向感知。此外，向后游动时身体前部的肌肉应变比向前游动时高得多。步长和推进效率的值表明，向后波动式游动在机械效率上低于向前游动。我们认为，典型的鳗鲡形身体形状是一个重要特征，它使这些动物能够利用一种类似于向前波动式游动机制的波动机制向后游动。大多数其他鱼类，如果能向后游动的话，也是通过鳍的摆动或波动来实现的。
