Museum of Comparative Zoology, Harvard University, 26 Oxford St., Cambridge, Massachusetts 02138.
Integr Comp Biol. 2002 Nov;42(5):1009-17. doi: 10.1093/icb/42.5.1009.
The median fins of fishes consist of the dorsal, anal, and caudal fins and have long been thought to play an important role in generating locomotor force during both steady swimming and maneuvering. But the orientations and magnitudes of these forces, the mechanisms by which they are generated, and how fish modulate median fin forces have remained largely unknown until the recent advent of Digital Particle Image Velocimetry (DPIV) which allows empirical analysis of force magnitude and direction. Experimental hydrodynamic studies of median fin function in fishes are of special utility when conducted in a comparative phylogenetic context, and we have examined fin function in four ray-finned fish clades (sturgeon, trout, sunfish, and mackerel) with the goal of testing classical hypotheses of fin function and evolution. In this paper we summarize two recent technical developments in DPIV methodology, and discuss key recent findings relevant to median fin function. High-resolution DPIV using a recursive local-correlation algorithm allows quantification of small vortices, while stereo-DPIV permits simultaneous measurement of x, y, and z flow velocity components within a single planar light sheet. Analyses of median fin wakes reveal that lateral forces are high relative to thrust force, and that mechanical performance of median fins (i.e., thrust as a proportion of total force) averages 0.35, a surprisingly low value. Large lateral forces which could arise as an unavoidable consequence of thrust generation using an undulatory propulsor may also enhance stability and maneuverability. Analysis of hydrodynamic function of the soft dorsal fin in bluegill sunfish shows that a thrust wake is generated that accounts for 12% of total thrust and that the thrust generation by the caudal fin may be enhanced by interception of the dorsal fin wake. Integration of experimental studies of fin wakes, computational approaches, and mechanical models of fin function promise understanding of instantaneous forces on fish fins during the propulsive cycle as well as exploration of a broader locomotor design space and its hydrodynamic consequences.
鱼类的中间鳍包括背鳍、臀鳍和尾鳍，长期以来一直被认为在鱼类稳定游动和机动时产生游动动力方面发挥着重要作用。但是，这些力的方向和大小、产生这些力的机制以及鱼类如何调节中间鳍力在很大程度上仍然未知，直到最近数字粒子图像测速（DPIV）的出现，这使得对力的大小和方向的实证分析成为可能。在比较系统发育学的背景下，对鱼类中间鳍功能的实验水动力研究特别有用，我们已经检查了四个硬骨鱼分支（鲟鱼、鳟鱼、太阳鱼和鲭鱼）的鳍功能，目的是检验经典的鳍功能和进化假说。在本文中，我们总结了 DPIV 方法学的两个最新技术进展，并讨论了与中间鳍功能相关的关键最新发现。使用递归局部相关算法的高分辨率 DPIV 允许量化小涡，而立体 DPIV 则允许在单个平面光片内同时测量 x、y 和 z 流速分量。对中间鳍尾流的分析表明，侧向力相对于推力力很高，并且中间鳍的机械性能（即推力作为总力的比例）平均为 0.35，这是一个令人惊讶的低值。使用波动推进器产生推力时可能不可避免地产生的大侧向力也可能增强稳定性和机动性。对蓝鳃太阳鱼软背鳍水动力功能的分析表明，产生了一个占总推力 12%的推力尾流，并且尾鳍的推力生成可能会通过拦截背鳍尾流而得到增强。中间鳍尾流的实验研究、计算方法和中间鳍功能的机械模型的整合有望实现对鱼类鳍在推进周期中瞬时力的理解，并探索更广泛的运动设计空间及其水动力后果。
