Almost everything long known about Regalecus glesne came from dead or dying animals washed ashore, which gave no reliable picture of behaviour. Observations from remotely operated vehicles and from divers over the past two decades have recorded living oarfish oriented vertically in the water column, head uppermost, the body held straight.
Movement comes from the dorsal fin. The fish passes waves along the long red fin while the body stays comparatively rigid, a swimming mode called amiiform locomotion. The vertical posture may help the fish scan for the small crustaceans and other plankton it feeds on, silhouetted against downwelling light.
The oarfish's other reputation, as an earthquake herald, does not hold up. A 2019 analysis comparing Japanese records of deep-sea fish appearances with subsequent seismic activity found no meaningful association, and strandings are better explained by illness, storms and currents.