About a Worm

Researchers hone in on parasite-ridden Klamath River hotspots

| February 08, 2007

A mid last week's news that the fed-eral government has mandated in-stallation of fish ladders as a condition of the government's relicensing of PacifiCorp's Klamath dams, some of the region's top fisheries scientists gathered in Fortuna to talk about a worm.

They met for two days to swap information about a tiny, translucent, squid-shaped class of worm known as a "polychaete" - specifically, Manayunkia speciosa, which studies have found to play a key role in the ongoing mass die-offs of juvenile Chinook salmon on the Klamath River. (These juvenile deaths are not to be confused with the 2002 adult fish die-off that grabbed everyone's attention, which involved a different set of problems.)

The scientists noted in passing the federal fish prescriptions for dam relicensing, but they were more excited by breakthrough studies that have been conducted by Oregon State University researchers out of Corvallis on the juvenile fish deaths. The OSU folks have been focusing on the Klamath's outmigrating juvenile Chinook, who've been dying in high numbers each spring from infection by a parasite called Ceratomyxa shasta - 40 to 90 percent of the juveniles die before they can reach the ocean. And the buzz during the cocktail hour after Wednesday's presentations was particularly infused with praise for what that young Rick Stocking of OSU had found while scraping about underwater in the Klamath looking for the worm that is the intermediary host to C. shasta.

Scientists have known for a couple decades that C. shasta causes ceratomyxosis, a fatal disease, in Pacific Northwest trout and salmon. Tribal fisheries biologists on the Klamath first noticed the juvenile deaths from C. shasta infection in the early 1990s. Scientists have also known, for years, about the presence of the polychaete worm.

But it wasn't until 1997 that microbiologist Jerri Bartholomew, of OSU's Center for Fish Disease Research, and her team of researchers discovered that C. shasta requires the polychaete worm, in addition to the salmon, to complete its life cycle. Her lab has also used cutting-edge DNA techniques to pinpoint occurrences of C. shasta's spores in the Klamath River - they found spores throughout the river, with some locations containing an especially high quantity. But still nobody knew much about the worm. Which is where Stocking came in.

"In 2003, [Bartholomew] posted a position for a graduate student to investigate where the polychaete is in the river, and what habitat it lives in," said Stocking, after the conference. "And I was interested in host-parasite ecology in an environment and, if that environment changes, how does it interfere with the host-parasite interaction? The Klamath was the perfect setting, because the Klamath River is a nutrient-rich system that has been modified."

Stocking said he knew that parasites had become a huge issue in fish farms. "I was curious, because fish seemed to be doing pretty well out in the environment - at least before we started mucking around with rivers. Whereas in the hatchery systems, they battle with [the parasites] every year. There's crowding and a lot of opportunities for pathogens to move from fish to fish, and the fish are stressed out."

So what exactly was going on in the Klamath?

"My thought was, it might have to do with the worm," Stocking said. "Maybe there were more polychaete worms, or maybe it was that these polychaetes were more infested, or both. And Jerri was also wondering if perhaps the hydroelectric dams had something to do with the distribution and abundance of the polychaete. Nobody knew."

So Stocking took the position at OSU, and finding the worm in the river became the basis for his master's thesis. His research was two-part. In one project, conducted between 2003 and 2006, he and fellow researchers put "sentinel" (test) fish in cages in the river at a number of locations above and below Iron Gate Dam. They used rainbow trout, known to be highly susceptible to C. shasta, as well as native stocks of hatchery-raised Chinook who'd never been in the river. Above the dam, infection was high in the rainbows but few of them died, and the Chinook showed little infection, proving their native high resistance to the parasite. Below the dam, said Stocking, all of the sentinel rainbow trout died from the infection, as did 50 percent of the sentinel Chinook. So even native stocks of Chinook, who've developed a resistance through time to the also native parasite C. shasta, were being overwhelmed somehow below the dam.

"This fascinated [Bartholomew]," said Stocking. "Why are those very-resistant fish dying? And what we found out was that the parasite below Iron Gate was so abundant that it was overwhelming the fish's resistance."

The only time there was little to no mortality among the test fish below the dam was during the wet year 2005-2006, which Stocking said suggests perhaps high spring flows flushed the parasite spores - and/or the worms - out of the hotspots where they were in abundance.

The second part of Stocking's project was investigating those hotspots, and non-hotspots, to gather distribution and abundance data on the parasite's second host, the worm: "getting in the water, looking around, scraping substrates, bottoms, sides, rocks, looking at vegetation in the weedy places, at the mud in the reservoirs - I sampled everything." He found that the polychaete worm is active throughout the main stem of the Klamath River, especially in pools, eddies and reservoirs. "I looked above and below the dam, and what I found was very revealing. The percentage of the population of worms that were infected throughout the Klamath was very, very low, about .01 percent. However, the populations immediately below Iron Gate were heavily infected, between 5-12 percent. So, hundreds of thousands of worms were infected below Iron Gate. The question is, why? And we've never identified for sure why that is. However, we have a pretty good guess."

Tribal and federal fishery biologists told the OSU researchers there was a high density of spawning areas just below the dam. Stocking and his crew concluded that the adult spawners, as they lay dying, were releasing C. shasta spores, which they'd picked up as they entered the river from the ocean, and the spores were raining down in great quantities onto the worms.

"So the adult salmon are the delivery mechanism in the parasite's life cycle," Stocking said.

In that life cycle, the parasite develops inside a salmon. It doesn't seem to affect adult salmon, who are dying anyway. And when the spawners die, the parasites are released into the water and have to next infect a polychaete worm. It is thought the worms eat them unwittingly, along with whatever else they encounter that's food-like. Inside the worm, the parasites multiply and are released. Once back in the water, the triangle-shaped parasite spores need to run into salmonids to proliferate - and in the spring, here come the juvenile Chinook freshly released from the Iron Gate hatchery and having to swim right through the thick soup of C. shasta spores.

"We're not sure how the entry is into the fish, whether through the skin or the gills," said Stocking. "But we do know that upon contact with the fish the spore shoots out a harpoon into the fish. And from there it works its way in. Once in, it works its way into the guts. It multiplies itself, dividing and dividing and dividing and consuming the fish's tissue. And the fish starts bleeding out - hemorrhaging."

The juveniles are hit hard, their immune systems overreact and they die. "And it's all traced back to that one spot below Iron Gate -- a 16-mile stretch," said Stocking.

At the fish health conference, Stocking and the other researchers who'd presented results of related studies, acknowledged that there is much more research to be done before they fully understand the polychaete worm. Some said perhaps they need to figure out how to bolster the Chinook's immune system against C. shasta. Others said maybe they could eradicate the parasite from the river - but Stocking said that doesn't make sense, because the parasite is a native. Others said perhaps the timing of the Chinook's migration runs could be manipulated to avoid the onslaught of spores. Maybe flows below the dam could be manipulated - perhaps with a high spring pulse. Or, maybe, somehow, the polychaete hosts could be "dried out" in the hotspots - they seem to fare poorly in very low flows.

But they all agreed on a couple of items. One, if PacifiCorp ends up deciding to take down the dams rather than to put in costly fish ladders, continued study will still be essential because it provides baseline data. And, two, that they need a stable and prolonged source of funding - and for that, they said, they were relying on the federal and state agencies for validation and cooperative research, and on the ocean harvesters for their ability to lobby for and attract funds. Government agents and ocean harvesters at the fish health conference seemed willing to work together - which also was somewhat of a breakthrough.

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