Virus found in Wisconsin trout

Trout swim in a viewing pond at the Nevin Hatchery in Fitchburg near Madison, where some fish tested positive for cutthroat trout virus. Photo: Rory Linnane, Wisconsin Center for Investigative Journalism

Trout swim in a viewing pond at the Nevin Hatchery in Fitchburg near Madison, where some fish tested positive for cutthroat trout virus. Photo: Rory Linnane, Wisconsin Center for Investigative Journalism

By Rory Linnane
Wisconsin Center for Investigative Journalism

State natural resource officials are wondering how a mysterious virus found its way to Wisconsin trout and what it will mean for the health of aquatic life.

“It’s a big unknown,” said Susan Marcquenski, a fish health specialist for the state Department of Natural Resources. “There’s very little information about the effect of the virus on cool-water species.”

Despite the uncertainty, state authorities confirm that they released 270,000 brown trout this year from hatcheries where fish tested positive for the cutthroat trout virus. An additional 160,000 had already been released last year before officials got the test results.

Raised in state hatcheries, the trout were meant to bolster the species’ population in local watersheds. They were the first fish known to be infected with the virus east of the Mississippi River, according to Marcquenski, though the virus may have previously gone undetected.

Because only samples of fish are tested, officials do not know how many of these fish were carrying the virus when released into the headwaters of the Mississippi and the Yahara river system.

Part of the rationale for releasing the infected fish was the benign history of the virus, which has been found in several western states. Though similar to the virus that causes Hepatitis E in humans, it has no known health impacts on the trout it inhabits, and likely cannot spread to mammals.

But little is known about the potential for the virus to spread to other cold-blooded animals that share a home with trout, such as pike, bass, other species of fish, and even amphibians.

At the Nevin Hatchery in Fitchburg near Madison, thousands of trout were released into the wild before officials learned some of the fish had tested positive for cutthroat trout virus. Photo: Rory Linnane, Wisconsin Center for Investigative Journalism

At the Nevin Hatchery in Fitchburg near Madison, thousands of trout were released into the wild before officials learned some of the fish had tested positive for cutthroat trout virus. Photo: Rory Linnane, Wisconsin Center for Investigative Journalism

“We definitely need more research,” Marcquenski said.

She and a professor at the University of Florida, Thomas Waltzek, are developing a proposal to study the effect of the virus on other fish species. Waltzek is also helping the DNR develop ways to track and remove cutthroat trout virus from fish eggs.

Wisconsin DNR officials first found the virus in November in lab results for brown trout at the St. Croix Falls Hatchery, analyzed by the U.S. Fish and Wildlife Service. The virus was also found at the Nevin Hatchery in Fitchburg near Madison and in trout from Lake Michigan.

“It’s quite a puzzle to us,” said Al Kaas, chief of DNR’s fisheries culture section. “We’ve been trying to figure out how our biosecurity measures broke down and allowed it to show up in three different locations in Wisconsin.”

The virus may have come to the state by people moving fish and fish eggs, or natural movement of fish and predators, Macquenski said. Sometimes birds pick up fish from neighboring waterways and drop them in the state’s exposed hatcheries.

Marcquenski said DNR officials, after consulting with the Wisconsin Department of Agriculture, Trade and Consumer Protection, as well as DNR’s Fish Management Board, released a group of trout likely carrying the virus.

“They chose not to take any regulatory action,” Marcquenski said. “So the fish were stocked in the watershed surrounding the St. Croix Falls Hatchery.” Kaas noted that none of the hatchery fish died or experienced adverse effects from the virus.

That watershed runs from the headwaters of the Mississippi River down to the Gulf of Mexico.

Jim Winton, a supervisory research microbiologist at the Western Fisheries Research Center in Seattle who specializes in fish viruses, said he was not seriously concerned about the DNR’s decision.

Although Winton said a precautionary principle is to not move fish that are carrying a virus, he noted that the virus may have already naturally migrated to the watershed.

“The fish either had it or acquired it from a local source,” Winton said. “If the virus was already in the watershed, it’s pretty hard to put that genie back in the bottle.”

 

The nonprofit Wisconsin Center for Investigative Journalism (www.WisconsinWatch.org) collaborates with Wisconsin Public Radio, Wisconsin Public Television, other news media and the UW-Madison School of Journalism and Mass Communication.

All works created, published, posted or disseminated by the Center do not necessarily reflect the views or opinions of UW-Madison or any of its affiliates.

6 thoughts on “Virus found in Wisconsin trout

  1. It makes perfect sense in that both the cause and effect seem unknown. Acting upon immediate facts seems to be the best recourse. A course of action taken upon unknown variables with unknown results is logically irrelevent.

  2. No comments? I am not really being sarcastic, every invasive species is like a disease and infection. Intentionally increasing alewives increases the disease, with a known affect. So planting diseased fish makes perfect sense, in a warped kind of way. Maybe it will kill a few Asian carp, but that’s unknown isn’t it.

  3. So we can quit worrying about VHS now? Only killed a few thousand fish, only a threat to hatchery that I can see. No way will VHS dominate and control the lakes. Other diseases been around for thousands of years, killed more. Alewives kill more native fish in a year than all these “diseases” can kill in a hundred years. The difference is?

  4. There are many things that were not “likely” to happen that have actually happened. Shocker. Fukushima anyone? We are always, unwisely, at the edge of our technology and understanding. You’d think we’d understand by now when we are balancing on the razor’s edge.

  5. There are many unknowns in this world, but since the virus has no known health impacts on the trout it inhabits, and likely cannot spread to mammals, that’s hundreds of thousands of dollars of trout — maybe a million dollars, who knows nowadays? — that they certainly didn’t want to waste. Can’t say I blame them, and sounds like the researcher in Seattle wasn’t too concerned either.

  6. If the source of the virus is unknown, and the full effects of the virus are unknown as well, wouldn’t it be more prudent not to release infected fish into local waterways?

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