鲫鱼C形起动的运动学特征分析

The Kinematic Analysis of C-start in Crucian Carp (Carassius Auratus)

快速起动是鱼类很重要的一种机动能力,有助于鱼类的逃逸和捕食。快速起动通常分为C形起动和S形起动两种模式。本文利用数字式高速摄像机定量地研究了鲫鱼为逃避危险从静止状态做逃逸反应的运动过程。观察发现所有的逃逸反应都是C形起动。仔细分析运动图像后,根据质心和尾鳍的运动,发现C形起动过程大体可以分解为三个阶段。第一阶段,质心保持不动,鱼体在极短的时间内绕质心弯曲呈C形,尾鳍同时迅速摆动;第二阶段,尾鳍作大幅度反向摆动,鱼头转动接近至最终方向;第三阶段,质心沿最终方向作直线运动。本文通过软件分析得到了各个阶段内鱼体躯干曲线的形状,进而给出了鱼体的速度和转动角速度分布,并从力学的角度定性地解释了机动过程。

Fast-starts are an important maneuver capability for most fish to escape from predators and for some fish to capture prey. The fast-starts can be divided into two main types, C-start and S-start. In this paper, the distance-time performance in escape response of startled Crucian carp (Carassius auratus) was investigated by employing high-speed digital video (1000Hz). All escape response observed are C-type fast-starts, in which the fish assumes a C shape at the end of the initial body contraction (stage 1). Examination of filmed sequences of turning fish shows that the C-type fast-start process includes three stages, distinguished by different movements of the centre of mass and motions of the caudal fin. In the first stage the centre of mass keeps the position, and the fish body turns a C shape, which leads the tail moves quickly. Next, the fish tail starts moving with large amplitude in the counter direction and the fish head turns into the final direction. At the last, the centre of mass moves in straight line of swimming. The curved figures of backbone of fish in all stages are given by using the special software. Distribution of the velocity along the backbone of fish and angle velocity of fish body around the center of mass are also obtained. Then, the whole escape response process is qualitatively analyzed from the point of view of hydrodynamics.