Scientists from University of California, Santa Barbara dissected the carcass of the 18-foot serpent-like creature and found large, larval tapeworms and adult spiny-headed worms in its intestine.
Scientists say the discovery of parasites could reveal what the oarfish's natural enemies are and where the elusive creature lives and hunts for food.
However, their report did not indicate how the oarfish died.
A snorkeler found the carcass of the oarfish Oct. 13. Several days later, another oarfish washed ashore in Oceanside.
The rarely seen deep sea-dwelling creatures can grow to more than 50 feet.
The Associated Press contributed to this report.
