Kinematics of the ribbon fin in hovering and swimming of the electric ghost knifefish

Ricardo Ruiz-Torres, Oscar M. Curet, George V. Lauder, Malcolm A. MacIver*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

51 Scopus citations


Weakly electric knifefish are exceptionally maneuverable swimmers. In prior work, we have shown that they are able to move their entire body omnidirectionally so that they can rapidly reach prey up to several centimeters away. Consequently, in addition to being a focus of efforts to understand the neural basis of sensory signal processing in vertebrates, knifefish are increasingly the subject of biomechanical analysis to understand the coupling of signal acquisition and biomechanics. Here, we focus on a key subset of the knifefish's omnidirectional mechanical abilities: hovering in place, and swimming forward at variable speed. Using high-speed video and a markerless motion capture system to capture fin position, we show that hovering is achieved by generating two traveling waves, one from the caudal edge of the fin and one from the rostral edge, moving toward each other. These two traveling waves overlap at a nodal point near the center of the fin, cancelling fore-aft propulsion. During forward swimming at low velocities, the caudal region of the fin continues to have counter-propagating waves, directly retarding forward movement. The gait transition from hovering to forward swimming is accompanied by a shift in the nodal point toward the caudal end of the fin. While frequency varies significantly to increase speed at low velocities, beyond approximately one body length per second, the frequency stays near 10Hz, and amplitude modulation becomes more prominent. A coupled central pattern generator model is able to reproduce qualitative features of fin motion and suggest hypotheses regarding the fin's neural control.

Original languageEnglish (US)
Pages (from-to)823-834
Number of pages12
JournalJournal of Experimental Biology
Issue number5
StatePublished - Mar 2013


  • Aquatic locomotion
  • Gymnotiform swimming
  • Swimming gait transition

ASJC Scopus subject areas

  • Insect Science
  • Ecology, Evolution, Behavior and Systematics
  • Aquatic Science
  • Animal Science and Zoology
  • Molecular Biology
  • Physiology


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