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Three-Dimensional Analysis of Finlet Kinematics in the Chub Mackerel (Scomber japonicus)

Department of Organismic and Evolutionary Biology, Harvard University, 26 Oxford Street, Cambridge, Massachusetts 02138

* To whom correspondence should be addressed. E-mail: jnauen{at}oeb.harvard.edu.

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° 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° 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° with the xz plane, while the distal portion of this finlet is oriented at 110°. 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.

This article has been cited by other articles:

				J. C. Nauen and G. V. Lauder Hydrodynamics of caudal fin locomotion by chub mackerel, Scomber japonicus (Scombridae) J. Exp. Biol., June 15, 2002; 205(12): 1709 - 1724. [Abstract] [Full Text] [PDF]

				J. C. Nauen and G. V. Lauder Locomotion in scombrid fishes: visualization of flow around the caudal peduncle and finlets of the chub mackerel Scomber japonicus J. Exp. Biol., January 7, 2001; 204(13): 2251 - 2263. [Abstract] [Full Text] [PDF]