Breakthrough: First Contagious Cancer Found in Fish Species

WHO:

Gizmodo - Researchers from Vermont, including co-lead researcher Julie Dragon, an associate professor of microbiology and molecular genetics at the University of Vermont.

WHAT:

Gizmodo - The researchers found that the transmissible cancer has been identified in catfish populations in other ponds and lakes across New England, including areas without major human-made sources of pollutants.

Phys.org - The cancer cells behave more like parasites than conventional tumors, moving from fish to fish.

NPR - "It is the infectious agent itself," says Julie Dragon, a data scientist at the University of Vermont and a co-author on the study. "Those cells can somehow escape the host, maybe live in the environment — the aquatic environment — and then infect a new host."

Gizmodo - The researchers found that the transmissible cancer has been identified in catfish populations in other ponds and lakes across New England, including places with no major human-made sources of pollutants.

Phys.org - Currently, 30% of catfish in Lake Memphremagog are reported to have melanoma tumors.

NPR - "It looks like black tar on the skin — not very pretty," says Peter Emerson, a fish biologist with the Vermont Fish & Wildlife Department.

Phys.org - Currently, 30% of catfish in Lake Memphremagog are reported to have melanoma tumors.

Gizmodo - The researchers found that over 30% of catfish in Lake Memphremagog have melanoma tumors.

NPR - The Vermont Fish & Wildlife Department reported that just over a quarter of the catfish had black blotches, which appeared suddenly the year prior to the census.

Gizmodo - A contagious form of cancer has been discovered in brown bullhead catfish (Ameiurus nebulosus) in Lake Memphremagog.

Phys.org - The cancer cells behave more like parasites than conventional tumors, moving from fish to fish.

Gizmodo - By 2014, roughly a third of catfish in the area had blackened skin lesions.

Gizmodo - This is the fourth known type of transmissible cancer discovered in animals.

WHERE:

Gizmodo - Lake Memphremagog, a freshwater lake that stretches from Quebec, Canada, to Vermont.

Phys.org - Other lakes across New England and Canada have also reported similar cases of the cancer.

WHEN:

Gizmodo - The researchers published their findings in a paper in Nature on a Wednesday.

Gizmodo - The first scientific reports of melanoma in brown bullhead catfish date back to the early 20th century.

WHY:

Gizmodo - The researchers suspect that the cancer may primarily spread during the spawning season when catfish aggregate and may scratch each other, allowing cancer cells to invade new hosts.

Gizmodo - The researchers suspect that the cancer may spread during the spawning season when catfish aggregate and may scratch each other, allowing cancer cells to invade new hosts.

Gizmodo - The researchers suspect that the cancer has shifted into a parasite-like entity that spreads among catfish.

Gizmodo - The cancer does not pose any danger to humans, but it raises questions about the long-term population health of brown bullhead catfish.

HOW:

NPR - "Over time, genome sequencing got cheaper and easier to do," says Julie Dragon, a data scientist at the University of Vermont and a co-author on the study.

NPR - The researchers conducted whole genome sequencing of the tumors, revealing that the tumors were genetically distinct from their host fish, indicating a transmissible nature.

Phys.org - The researchers conducted whole genome sequencing of the tumors, revealing that the tumors were genetically distinct from their host fish, indicating a transmissible nature.

Gizmodo - Researchers conducted genetic analyses of tumors from affected fish and compared them to healthy tissue from the same fish and other unaffected catfish.

Gizmodo - Whole-genome sequencing of the tumors revealed hundreds of thousands of genetic variants shared among the tumors that were not found in the fish hosts.

(UPDATED July 23, 2026 14:43 UTC)

Researchers have discovered a transmissible cancer affecting catfish populations in various ponds and lakes across New England, even in areas without significant human-made pollutants. The cancer cells act more like parasites, moving from one fish to another, and may primarily spread during the spawning season when catfish gather and come into contact with each other. According to Julie Dragon, a data scientist at the University of Vermont and a co-author of the study, advancements in genome sequencing technology have made it easier to study these infectious agents.

(UPDATED July 23, 2026 05:53 UTC)

Researchers have identified a transmissible cancer affecting catfish populations in various ponds and lakes across New England, even in areas without significant human-made pollutants. Currently, around thirty percent of catfish in Lake Memphremagog are reported to have melanoma tumors, which appear as black tar on their skin, according to fish biologist Peter Emerson. The study's co-author, Julie Dragon, noted that advancements in genome sequencing have made it cheaper and easier to conduct this type of research.

(UPDATED July 22, 2026 23:21 UTC)

Researchers have identified a transmissible cancer affecting catfish populations in various ponds and lakes across New England, including areas without significant human-made pollutants. In Lake Memphremagog, about thirty percent of catfish are reported to have melanoma tumors, and the cancer is believed to spread primarily during the spawning season when the fish gather and may come into contact with one another. Whole genome sequencing of the tumors has shown that they are genetically distinct from the host fish, confirming their transmissible nature.

(UPDATED July 22, 2026 22:22 UTC)

Researchers have discovered that over 30% of catfish in Lake Memphremagog are affected by melanoma tumors, with the Vermont Fish & Wildlife Department noting that just over a quarter of these fish displayed sudden black blotches last year. The scientists believe that the cancer may spread during the spawning season, as catfish gather and may inadvertently scratch each other, facilitating the transfer of cancer cells. Whole genome sequencing of the tumors has shown that they are genetically distinct from the host fish, suggesting a transmissible nature of the disease.

(UPDATED July 22, 2026 19:27 UTC)

Researchers from Vermont, led by Julie Dragon, have discovered a contagious form of cancer in brown bullhead catfish in Lake Memphremagog, which stretches from Quebec to Vermont. This cancer behaves more like a parasite than a traditional tumor, spreading from fish to fish, and has been linked to blackened skin lesions observed in about a third of catfish in the area by 2014. The findings, published in a paper in Nature, reveal that this is the fourth known type of transmissible cancer in animals, raising concerns about the long-term health of the catfish population, although it poses no danger to humans.