Why does Gymnarchus swim with its body held straight?

Gymnarchus swims with its body held straight to maintain the stability of its electrical navigation and detection system.1

Because the fish's electric organs are located near its tail, standard swimming movements—which involve side-to-side undulations of the tail—would constantly shift the position of the electric field relative to the receptor organs located in the head area. By keeping the body rigid and relying on undulations of the dorsal fin for propulsion, Gymnarchus ensures that its sensory apparatus remains stable, allowing it to effectively detect objects and navigate through the turbid waters it inhabits.1