A massive oarfish that was found washed ashore in Southern California last month was filled with parasites, says a team of researchers who dissected the creature earlier this week – a finding that provides scientists with valuable insight into the mysterious deep-sea creature.

The five-metre long oarfish was found dead by a snorkeler near Catalina Island, just south of the Los Angeles coastline, on Oct. 13. More than 15 helpers were needed to drag the giant creature ashore.

The surprising discovery intrigued many marine biologists since the elusive oarfish is known to commonly dwell in deep waters up to 900 meters below the surface. They very rarely come to the water’s surface.

And just days later, another slightly smaller oarfish was discovered near the coast of San Diego. That four-meter-long fish was found to be carrying thousands of mature eggs.

Parasitologists from the University of California Santa Barbara were so captivated by the rare discoveries that they asked for tissue samples from the Catalina oarfish.

It was then they discovered the fish to be carrying its own “little monsters” -- a large number of parasites.

"These (findings) tell you about what the natural enemies of the oarfish are," Dr. Armand Kuris said in a statement.

Kuris, a professor of zoology at UCSB, added that the rare discovery gives scientists valuable clues into the ecology and habitat of the deep-water fish.

"In this little piece of intestine that we had, we found quite a few of these rather large larval tapeworms. One of them was about 15 centimetres long."

Despite the fact researchers had only a small portion of the fish’s intestine, spleen and gallbladder to work with, Kuris said they were able to come away with a lot of information.

"This thing had all sorts of stuff in it, even when we had almost no actual tissue to work with," Kuris wrote in his statement.

The oarfish -- also known as the ribbonfish -- is thought to be the world's largest bony fish and can grow to lengths of more than 15 meters. However, because the serpent-like fish lives in deep waters, relatively little is known about the creature.

While the cause of death of the two fish remains unclear, experts say it is possible the fish ventured too close to shore and were swept in by strong waves.

"Oarfish wash ashore, one every few years," said Kuris, adding that finding such a fish that hasn't rotted or been eaten by other organisms is "the result of many uncommon events."

Scientists hope to learn even more about the elusive oarfish by analyzing samples of the parasites and running DNA analysis on the specimens.