Oarfish hosted parasites, giving scientists insight into bony fish

Researchers have discovered that the massive oarfish hosts several types of parasites, revealing clues about the serpent-like fish’s habitat, UC Santa Barbara announced this week.

Parasitologists at the university obtained small tissue samples -- gills, intestine, stomach, spleen and gallbladder -- from the 18-foot creature that was found dead in shallow water just off Catalina Island on Oct. 13. They discovered larval tapeworms and pieces of a spiny-headed worm embedded in the intestine dissected at the university.

Parasites found in the animal provide insight into what the fish eats and what its predators are because the organisms spend stages of their life cycles in various hosts, said Armand Kuris, professor of zoology in the UCSB Department of Ecology, Evolution and Marine Biology.

The tapeworms, usually found in sharks in their adult form, will remain larva until the oarfish is eaten and they mature into their next stage, he said, which suggests large sharks prey on the bony fish.

The spiny-headed worm found in the fish was an adult, suggesting the oarfish ate its host, likely krill or another deep-water crustacean.


“This thing had all sorts of stuff in it, even when we had almost no actual tissue to work with,” Kuris said.

Little is known about the world’s largest bony fish, which live in deep waters and are not often seen alive. What is known comes from the few carcasses that have washed ashore.

Parasites in the oarfish haven’t been examined for years – the last substantial publications about them are 50 years old, Kuris said.

Researchers will next send the parasites for further examination and possibly molecular DNA analysis.

“If all you knew about deer was road kill … how much would you actually know about deer?” said Milton Love, a research biologist at the Marine Science Institute at UC Santa Barbara. “That’s kind of where we are with oarfish.”

The 18-foot giant found off Santa Catalina Island was among the largest oarfish reported in nearly 20 years. A 14-foot fish was beached in Oceanside on Oct. 18.

What killed the two oarfish hasn’t been determined, but Love said he believes that the deaths are probably linked. The most likely cause was a current that carried the weak-swimming creature from still waters into a near-shore, more turbulent area, which they aren’t adapted to surviving in.

Despite its menacing appearance, the serpentine, silver fish is toothless and heavy, with weak, flabby muscles. It glows slightly, and a ribbon-like dorsal fin waves along the length of its body as it hangs in the water, sucking down plankton and jellyfish, said Russ Vetter, who assisted in the smaller fish’s dissection and directs the fisheries resource division at the Southwest Fisheries Science Center.

The tissue was divided and sent to research specialists around the world, who will look for clues about the creature and its habitat. The fish’s tissue will be tested for toxins, and data that could indicate low oxygen levels in the water will be examined as they become available, Vetter said.

“People from all around the world are desperate for a piece of tissue,” Vetter said.


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