Washed-Up Oarfish Reveal Secrets of the Deep to Scientists

Armand Kuris, professor of zoology, and graduate student researchers Sara Weinstein and John McLaughlin. Weinstein holds a 15 cm larval tapeworm found in the oarfish's intestine. | Photo: Sonia Fernandez

We still don't know whether there's something more than coincidence behind the two oarfish that washed up on Southern California beaches this month, but a wildlife lab in Santa Barbara has taken advantage of the opportunity to learn about oarfish ecology -- with the help of critters many Californians would probably rather not think about.

After receiving a few pieces of the internal organs of an 18-foot oarfish that a snorkeler found off Santa Catalina Island on October 13, researchers at UC Santa Barbara's Department of Ecology, Evolution and Marine Biology say they've learned a few things about how oarfish fit into the deep-sea food chain off the coast of California.

The keys to those discoveries? Parasites in the fish's intestines.

Oarfish, a.k.a Regalecus glesne, can reach lengths of up to 30 feet, putting them in contention for the title of the world's largest bony fish. But as they tend to stay 650-1,000 feet down beneath the surface of the ocean, they aren't commonly encountered, and so fisheries biologists rarely have the opportunty to study one.

According to UCSB zoology professor Armand Kuris, it's even more rare to find an oarfish that has any internal organs left for study: sea creatures usually make short work of anything even remotely edible. As a result, it's been a very long time since scientists have been able to study the fish's internal ecology: the roster of internal flora and fauna that make their living by parasitizing the oarfish. "The only substantial publication [on oarfish parasites] is fifty years old," says Kuris.

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Alerted by the oarfish's viral presence on the web, Kuris and UCSB fish biologist Milton Love obtained samples of the oarfish's intestines, gills, gall bladder, liver, spleen, and stomach. It wasn't a large proportion of the oarfish's remains, but Kuris and Love's team were able to find plenty of parasites to work with nonetheless.

Among the most interesting finds were two intestinal parasites that hint at the oarfish's place in the benthic food chain. The researchers found larval forms of a tapeworm species whose adult stage is commonly found in the guts of very large sharks. That suggests that those large sharks may well acquire those tapeworms by eating oarfish, whereupon the larvae metamorphose into adults.

The oarfish's intestines also provided clues as to the oarfish's relationships in the opposite direction on the food chain. While dissecting a section of intestine, UCSB graduate student Sara Weinstein discovered a piece of a spiny-headed worm embedded in the intestinal wall. Spiny-headed worms are a very large group of parasites related to rotifers that commonly infect crustaceans and their larvae. The adult spiny-headed worm in the oarfish suggests that the fish had eaten krill or other crustaceans.

Kuris describes that lab's work and preliminary findings in this video:

Samples of the fish's parasitic fauna have been sent to a lab for DNA analysis, and the team hopes to find a lot more data from the results of the genetic testing.

In the meantime, the work is a great reminder that wildlife exists in a lot of places we might not have thought about. There are thriving ecological niches everywhere we look in California, and some of those niches are inside of other Californians.

For ongoing environmental coverage in March 2017 and afterward, please visit our show Earth Focus, or browse Redefine for historic material.
KCET's award-winning environment news project Redefine ran from July 2012 through February 2017.

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