Department of Organismic Biology, Ecology, and Evolution, University of California, Los Angeles, California 91606.
Integr Comp Biol. 2002 Nov;42(5):971-80. doi: 10.1093/icb/42.5.971.
Boxfishes (Teleostei: Ostraciidae) are rigid-body, multi-propulsor swimmers that exhibit unusually small amplitude recoil movements during rectilinear locomotion. Mechanisms producing the smooth swimming trajectories of these fishes are unknown, however. Therefore, we have studied the roles the bony carapaces of these fishes play in generating this dynamic stability. Features of the carapaces of four morphologically distinct species of boxfishes were measured, and anatomically-exact stereolithographic models of the boxfishes were constructed. Flow patterns around each model were investigated using three methods: 1) digital particle image velocimetry (DPIV), 2) pressure distribution measurements, and 3) force balance measurements. Significant differences in both cross-sectional and longitudinal carapace morphology were detected among the four species. However, results from the three interrelated approaches indicate that flow patterns around the various carapaces are remarkably similar. DPIV results revealed that the keels of all boxfishes generate strong longitudinal vortices that vary in strength and position with angle of attack. In areas where attached, concentrated vorticity was detected using DPIV, low pressure also was detected at the carapace surface using pressure sensors. Predictions of the effects of both observed vortical flow patterns and pressure distributions on the carapace were consistent with actual forces and moments measured using the force balance. Most notably, the three complementary experimental approaches consistently indicate that the ventral keels of all boxfishes, and in some species the dorsal keels as well, effectively generate self-correcting forces for pitching motions-a characteristic that is advantageous for the highly variable velocity fields in which these fishes reside.
箱鲀（硬骨鱼纲：眶棘鲈科）是一种身体僵硬、多推进器的游泳者，在直线运动中表现出非常小的反冲运动幅度。然而，这些鱼类平滑游动轨迹的产生机制尚不清楚。因此，我们研究了这些鱼类的骨甲在产生这种动力稳定性方面的作用。测量了四种形态截然不同的箱鲀的甲壳特征，并构建了这些箱鲀的解剖精确立体光刻模型。使用三种方法研究了每个模型周围的流动模式：1）数字粒子图像测速法（DPIV），2）压力分布测量法，3）力平衡测量法。四种物种的甲壳的横截面和纵向形态都有明显差异。然而，这三种相互关联的方法的结果表明，各种甲壳周围的流动模式非常相似。DPIV 结果表明，所有箱鲀的龙骨都会产生强烈的纵向涡旋，这些涡旋的强度和位置随迎角而变化。在 DPIV 检测到附着、集中涡度的区域，压力传感器也检测到甲壳表面的低压力。使用力平衡测量实际力和力矩的预测结果与观察到的涡旋流动模式和压力分布对甲壳的影响一致。最值得注意的是，这三种互补的实验方法一致表明，所有箱鲀的腹龙骨，在某些物种中还有背龙骨，有效地产生了俯仰运动的自校正力，这一特征有利于这些鱼类所处的高度变化的速度场。
