How do mormyrid fishes swim with little movement of their bodies?

Mormyrid fishes swim with little body movement primarily to facilitate the use of their electrical organs, which are located near the tail.12

Because these fish rely on an electric field for navigation and detecting prey or obstacles in turbid water, keeping the body rigid prevents the tail from moving side-to-side. If the tail were to move in the traditional manner, it would constantly shift the position of the electric organs relative to the receptor organs located in the head, thereby disrupting the fish's sensory screen. Instead of using body undulations, these fish utilize their dorsal fins for propulsion, allowing them to maintain a straight body posture while moving.13