Nauen J C, Lauder G V
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
Biol Bull. 2001 Feb;200(1):9-19. doi: 10.2307/1543081.
Finlets, which are small non-retractable fins located on the body margins between the second dorsal and anal fins and the caudal fin of scombrid fishes, have been hypothesized to improve swimming performance. The kinematics of three posterior finlets of the chub mackerel, Scomber japonicus, were examined using three-dimensional measurement techniques to test hypotheses on finlet rigidity and function during steady swimming. Finlet bending and finlet planar orientation to the xz, yz, and xy planes were measured during steady swimming at 1.2 lengths s(-1) in a flow tank. Despite very similar morphology among the individual finlets, there was considerable variability in finlet flexure during a stroke. Several of the finlets were relatively rigid and flat (with intrafinlet angles close to 180 degrees during the stroke), although intrafinlet angle of the proximal portion of the most posterior finlet varied considerably over the stroke and was as low as 140 degrees midstroke. Finlets showed complex orientations in three-dimensional space over a stroke, and these orientations differed among the finlets. For example, during tail deceleration the proximal portion of the fifth finlet achieves a mean angle of approximately 75 degrees with the xz plane, while the distal portion of this finlet is oriented at 110 degrees. Our data suggest that the trajectory of local water flow varies among finlets and that the most posterior finlet is oriented to redirect flow into the developing tail vortex, which may increase thrust produced by the tail of swimming mackerel.
小鳍（位于鲭科鱼类第二背鳍与臀鳍之间以及尾鳍边缘的小型不可收缩鳍）被认为有助于提高游泳性能。运用三维测量技术研究了日本鲐鱼三个后部小鳍的运动学，以验证在稳定游泳过程中小鳍的刚性和功能假设。在流水槽中以1.2体长每秒（s(-1)）的速度稳定游泳时，测量了小鳍弯曲以及小鳍在xz、yz和xy平面的平面取向。尽管各个小鳍的形态非常相似，但在一个泳姿中小鳍弯曲存在很大差异。有几个小鳍相对刚性且扁平（在泳姿中鳍内角度接近180度），不过最后一个小鳍近端部分的鳍内角度在整个泳姿中变化很大，在泳姿中间位置低至140度。在一个泳姿中，小鳍在三维空间呈现复杂的取向，并且这些取向在不同小鳍之间存在差异。例如，在尾部减速时，第五个小鳍近端部分与xz平面的平均角度约为75度，而该小鳍远端部分的取向为110度。我们的数据表明，不同小鳍之间局部水流轨迹不同，并且最后一个小鳍的取向是将水流重新导向正在形成的尾涡，这可能会增加鲐鱼游泳时尾部产生的推力。
