Contagious Cancer Discovered in Vermont Catfish

Sitting on the border of Quebec and Vermont, Lake Memphremagog is one of the largest lakes in the Green Mountain State and a true angler’s paradise. With over 20 species of gamefish found in Memphremagog’s glacial waters, anglers flock to its shorelines to catch everything and anything from perch to salmon.

However, the recent discovery of a contagious melanoma that’s been discovered among Memphremagog’s brown bullhead population has tainted this fishing oasis.

A Cancerous Discovery

Back in 2011, anglers started reporting “black, tar-like” marks on the faces and bodies of bullhead they regularly caught in Lake Memphremagog, said Vermont Fish and Wildlife (VTFW) biologist Tom Jones.

As VTFW began to receive more photos from anglers reporting the strange marks, they decided to launch a study in 2013. The illness continued to spread, and by 2014, nearly one in three brown bullheads in Memphremagog were found with black lesions on their bodies. As brown bullheads are considered indicators of environmental quality, researchers originally believed that the black marks were caused by a pathogen or some sort of contamination that was possibly linked to pollution. However, they quickly discovered that the black marks were a form of contagious skin cancer.

“It’s pretty wild,” said VTFW Fish Health Biologist Matt Bodnar. “The only other contagious cancers known in the animal kingdom are found in dogs, Tasmanian devils, and one in bivalves. However, the tumor types are different for each, so this is the first one ever discovered that’s a melanoma.”

Once it was discovered that the black lesions found on the bullhead were cancer, VTFW and other researchers from the University of Vermont set out to find a potential cause and what could be done about it.

Researchers gather brown bullheads in Lake Memphremagog.

A Malignant Mystery

Unfortunately, the cancerous fish in Lake Memphremagog don’t seem to be fighting off the disease. This has led researchers to believe that this specific type of cancer is more complicated and even contagious.

“This cancer is contagious, so the cancer cells are acting much more like a parasite,” said Dr. Julie Dragon, a scientist at the University of Vermont and co-leader of a new study on the bullhead. “For this to happen and the immune system to not do anything about it, something else, some root cause, has happened as well. This could be pollutants suppressing the bullhead’s immune system. It could also be other mutations that make the fish unable to fight off the disease. We’re just not sure yet.”

Dr. Julie Dragon and other researchers have discovered that the cancer probably spreads among the fish when bullheads rub up against one another during spawning season. Generally, the cancer cells are found in larger fish of spawning age, which attributes to the theory.

The contagious nature of the cancer worries many of Memphremagog’s anglers, who fear the cancer could be spread to other popular gamefish in the lake, such as trout, bass, and landlocked salmon. But researchers have found, so far, that other species aren’t contracting it, and it isn’t transferable to humans.

“We’ve only found the melanoma in brown bullhead so far,” Bodnar told MeatEater. “BUT, so far the lakes we have confirmed the disease in don’t have other closely related species, like yellow bullhead, in them. It’s still an open question about whether this cancer affects different species, but it doesn’t appear to jump to any less related fish like bass or salmon.”

While this news should come as a relief for local anglers, the sudden emergence of the cancer is still incredibly disturbing. Research on this cancer is still underway, but it is possible that the disease isn’t exactly new.

“From what we’ve done so far, it looks like this cancer may have been noticed in the past,” Dragon told MeatEater. “We have past reports, even from as far back as 100 years ago, of similar lesions in the catfish but cannot absolutely confirm it’s the same thing at the time.”

Regardless of the cancer’s origins, researchers are working to get to the bottom of it.

Fishing for a Cure

Currently, VTFW is planning on a cohabitation study in the spring of 2027. Diseased bullhead will be cohabited with disease-free bullhead and observed and tested for disease transfer. Scientists will also study the survival of these melanistic cells in water.

“It will be critically important to follow through with these additional studies,” Jones told MeatEater. “We want to establish the role of potential environmental stressors and pollutants, both natural and human-induced.”

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