[2] The species can be distinguished by its red dorsal fin crests, light brown head, and scaleless, silver body.

[2] Older R. russelii often have a posterior stump-like tail, which is a consequence of self-amputation but show no signs of regeneration.

[4] It has also been hypothesized that this hyper ossification acts as a lever for the oarfish dorsal fins, which contributes to the organism's buoyancy.

[4] R. russelii's flaccid skeleton lacks mineralization, which is advantageous in maintaining buoyancy in deep waters.

[5] Researchers have been able to perform CT scans and rare, invasive studies on this structure of a deceased R. russelii to better understand its physiological significance.

Using photographs, histological cross-sections, and measurements of four samples of R. russelii, researchers were able to qualitatively describe the sexual organs of the species.

An analysis of these findings led researchers to conclude that R. russelii are likely batch spawning fish that produce a large number of offspring every breeding season.

[6] Based on a study that performed an artificial insemination with the eggs and sperm from a pair of deceased R. russelii samples, the morphology of the oarfish larvae was able to be examined.

[10] In June 2022, a juvenile was seen on the Great Barrier Reef off Queensland, Australia, by a snorkel tour leader.

[12][13] The low number of live sightings of oarfish has made it difficult to determine the precise distribution of the Regalecus, and further research is needed.

It feeds on euphausiid crustaceans, small fishes and squid, and uses its protrusile jaws to suck in prey.

[14] The oarfish mostly consumes a diet of krill[15] as its energy source, using its jaw to fill its oro-branchial cavity with the crustaceans, that will then be held in the gullet and passed through.

[20] Despite the relatively limited number of oarfish researched, in 2014 scientists were able to discover a new species of nematode called Spinitectus gabata (Spirurina: Cystidicolidae) within the gastrointestinal tract of a R. russelii off the coast of Japan.