Bathypterois grallator does not swim to hunt. It settles on the abyssal mud on three elongated rays, which raise the body clear of the bottom and hold it in a fixed orientation. Photographs from deep-sea vehicles repeatedly show individuals oriented into the prevailing current.
The forward-held pectoral fins carry an elaborate ray structure and are thought to detect small crustaceans drifting past, which the fish then takes in a rapid movement. Its eyes are very small and it lives well below the depth of useful sunlight, so tactile and hydrodynamic cues rather than sight appear to guide feeding.
At intervals the fish must stiffen those rays to stand and relax them to swim, and the fin rays are perfused with blood, which suggests the change in rigidity is actively controlled. The mechanism has been described anatomically but the details of how stiffness is regulated are still not fully worked out.