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Scientists hope genetics could tell them why these catfish in Lake Memphremagog have a rare cancer

A closeup of two fish being held in human hands, with the fish on the left bearing dark spots
Abagael Giles
Vermont Public
While collecting data back at the dock in Newport, Pete Emerson (left) holds up a brown bullhead with melanomas on the left, while a colleague holds up a healthy fish. Both were caught in Lake Memphremagog in May 2023.

On a research trip earlier this year, an electroshocking boat is putting a strong current out into the waters of Lake Memphremagog, the lake that spans the border between Vermont and Quebec.

The electricity is just enough to stun the fish, so they float to the surface, belly up. Scientists catch them in nets and plop them into holding tanks.

They’re looking for brown bullhead — a whiskered fish that likes to burrow in lake muck. The scientists want to test their skin, organs, blood and genes.

Pete Emerson, the state fisheries biologist for Vermont’s Northeast Kingdom, and others have found that between 35% and 45% of the mature brown bullhead in this lake have melanoma, a skin cancer. It’s super rare in fish, especially bottom feeders like these. In fact, this rate of cancer has never been documented in fish anywhere else.

A person wearing a baseball cap connects a piece of equipment on a boat
Abagael Giles
Vermont Public
A scientist with Vermont Fish and Wildlife hooks up the anode of the electrifishing boat on Lake Memphremagog. The boat delivers a shot to the water, and stuns fish, making it easier to catch them for research.

Anglers started reporting that they were catching fish with tumors about a decade ago. Scientists at first thought the bullhead might have a virus. But so far they haven’t found a smoking gun.

And while people in Vermont love to eat bullhead because they’re so tasty, that’s not the only reason scientists are worried about these fish.

Vicki Blazer is a fishery biologist with the U.S. Geological Survey, which is partnering with University of Vermont and Vermont Fish and Wildlife to try to find out what’s going on.

“Brown bullhead are a really good indicator species, particularly of sediment issues, and they've been used for for decades in the Great Lakes as an indicator species, so we have a lot of data on them," Blazer said.

Think of an indicator species as sort of like a thermometer for the lake’s health. A canary in a coalmine. Diagnose the fish, and you might find the pollutant.

Two people hold fish nets with fish inside
Abagael Giles
Vermont Public
Scientists with the USGS and Vermont Fish and Wildlife net stunned brown bullhead in a cove on Lake Memphremagog.

Vicki’s done all sorts of work with bullhead in polluted harbors in the Great Lakes and Chesapeake Bay. But Blazer says she’s never seen anything like what they’re finding on Memphremagog.

So far, they’ve tested fish tissue for PFAS — tiny, so-called forever chemicals. They’re testing the blood plasma, too.

They’ve also tested for about 60 other chemical contaminants, including pesticides, PCBs and heavy metals.

And they’ve tested for chemicals called polycyclic hydrocarbons, or PAHs. These chemicals are associated with gasoline and other fossil fuels, and they’ve been linked to fish cancers in the Great Lakes.

While most of the fish tested positive for PAHs, PCBs and PFAS, the scientists say the concentrations are too low to single out a chemical as the lone cause. And they found healthy fish with higher concentrations of both kinds of these chemicals at other Vermont lakes and rivers.

A control panel with knobs and labels, including a red switch that says "electrofisher emergency shutdown"
Abagael Giles
Vermont Public
The control panel on the electrifishing boat, where Pete Emerson with Vermont Fish and Wildlife controls the voltage put out into the lake.

Vicki Blazer with the USGS hopes genetics might point them towards the answer:

"There are certain genes that will indicate what they’ve been exposed to," Blazer said.

Genes can be turned on and off like switches. Sometimes a chemical contaminant or radiation can flip the switch. Sometimes a virus. Sometimes both.

To study that, you first need to know the genome of a healthy individual. And until this project, no one had ever mapped a brown bullhead genome.

Julie Dragon is a geneticist at the University of Vermont.

“We kind of liken it to a jigsaw puzzle, where you know, you’ve got the box as a reference, and you’re matching up pieces that you need," Dragon said. "You need the picture from the box.”

Next, Dragon and her team will compare the genetics of brown bullhead with cancer with the genetics of healthy fish, looking for places where they’re different.

A hand holds a fish covered in dark spots in front of a railing and lake
Abagael Giles
Vermont Public
A scientist moves a brown bullhead that has melanomas from a net and into the holding tank onboard the electrofishing vessel on Lake Memphremagog.

She says it’s looking for a needle in a haystack. It could take a long time, and it could be that more than one gene or more than one trigger is at play.

“It will not be easy to answer this question," Dragon said. "I would love to say that sequencing is the end-all be-all, but it’s not. I mean, it just gives us more to think about.”

But some people in the Northeast Kingdom say, regardless of what’s causing the cancer, there are steps the state could take now to improve water quality.

“I really insist that that is a really good reason not to ever deliberately or accidentally contaminate further the water of Lake Memphremagog," said Peggy Stevens, an organizer with the grassroots environmental watchdog group Don’t Undermine Memphremagog’s Purity, or DUMP.

There are a handful of industrial sites near Newport’s South Bay that DUMP and others think could be polluting it, like an old railroad yard.

A man stands above a landfill pit.
Jane Lindholm
VPR File
The landfill in Coventry.

And then there’s the Coventry landfill. State regulators have found that leachate from the landfill contains PFAS, and it used to go into the lake.

Peggy points out that for some of these chemicals, the EPA has essentially said that any exposure at all is unsafe for human health.

And while Peggy and DUMP do not blame the landfill for the bullhead cancer, she thinks it’s a warning sign that regulators need to do more to protect the lake.

"It’s just more about, let us, please, let's protect the lake from further contamination," Stevens said.

They’re also concerned because the state hasn’t made it crystal clear whether these tasty fish are still safe to consume.

For Pete Emerson with Fish and Wildlife, having the brown bullhead genome will be huge for diagnosing problems in polluted lakes all over the Northeast. And it could even tell scientists more about how chemicals like PFAS affect human tissue.

He’s hoping the cause is something fixable.

“People love to eat these fish," Emerson said. " I’m really nervous that it might be something that we can’t solve.”

He hopes they’ll get some answers in the next year or two.

Have questions, comments or tips?Send us a message.

Abagael is Vermont Public's climate and environment reporter, focusing on the energy transition and how the climate crisis is impacting Vermonters — and Vermont’s landscape.

Abagael joined Vermont Public in 2020. Previously, she was the assistant editor at Vermont Sports and Vermont Ski + Ride magazines. She covered dairy and agriculture for The Addison Independent and got her start covering land use, water and the Los Angeles Aqueduct for The Sheet: News, Views & Culture of the Eastern Sierra in Mammoth Lakes, Ca.