Meeting Abstract

P2.171  Tuesday, Jan. 5  Counter-Propagating Waves in the Ribbon Fin of Eigenmannia virescens Enhance Maneuverability SEFATI, S.*; FORTUNE, E.S.; COWAN, N.J.; Johns Hopkins University, Baltimore, MD; Johns Hopkins University, Baltimore, MD; Johns Hopkins University, Baltimore, MD shahin@jhu.edu

Ribbon-finned weakly electric knifefish, Eigenmannia virescens, are agile and maneuverable swimmers. A long undulating fin along the ventral side of the body of Eigenmannia generates the majority of its propulsive force. Several parameters of the undulating fin affect thrust force, some of which are fixed (e.g. the height of the fin is a fixed morphological parameter) while others are actively controlled to modulate thrust (e.g. frequency, amplitude and wavelength of undulation). Fin length may seem to be a fixed parameter, but Eigenmannia employ a mechanism for changing effective fin length. The fin motion is partitioned rostrocaudally with the two ends undulating in counter-propagating waves, hence generating antagonistic thrust forces. During station-keeping (or “hovering”), the fin is partitioned equally front-to-back; in forward swimming, the partition node moves caudally, generating a forward net thrust. Here, we investigated how Eigenmannia produce net thrust during steady-state forward swimming using high-speed videography of individuals swimming in a flow tunnel. We recorded video captured from fish behavior during different steady state flow velocities and we observed that frequency, amplitude, and wavelength of the two counter-propagating waves remain nearly constant over a range of 0-10 cm/s, but the node position moves from near the center of the fin toward the downstream end of the fish. These experiments strongly suggest that at these low swimming speeds, node position dominates differential thrust production. This strategy might enable fish to rapidly switch the direction of motion without the need to completely reverse wave propagation along the entire fin. Future work will investigate this directly by observing fin kinematics during transient movements and by simulation using computational fluid dynamics.