It was not until 2001 that an oarfish was filmed alive and in situ: the 1.5 metre fish was spotted by a group of US Navy personnel during the inspection of a buoy in the Bahamas[1]. The oarfish was observed to propel itself via an amiiform mode of swimming; that is, rhythmically undulating the dorsal fin whilst keeping the body itself straight. Perhaps indicating a feeding posture, oarfish have been observed swimming in a vertical orientation, with their long axes perpendicular to the ocean surface. In this posture the downstreaming light would silhouette the oarfishes' prey, making them easier to spot.
Is how they swim apparently, from wikipedia.