  The knifefish species propels itself by generating a reverse Karman street
from an anal fin and without significantly moving its body. This unique feature
makes this species' propulsion method highly efficient (Blake, 1983). It has
been suggested that there is an optimal swimming range for fish based on the
amplitude and frequency of the reverse K\'arm\'an street. Experiments have been
performed to measure the ratio between the amplitude and wavelength of vortices
in the wake of a knifefish. It is suggested that by optimizing the thrust
created by the reverse Karman street the wave efficiency can be estimated for a
given spacing ratio, and present observations have an average value of 0.89.
The relationship established between spacing ratio and wave efficiency, in
addition to the measured parameters, will be invaluable for bio-inspired
designs based on the knifefish.
