Researchers have discovered a transmissible melanoma-like cancer spreading among brown bullhead catfish in Lake Memphremagog [1].
This finding marks the first known instance of a contagious cancer appearing in a freshwater species. Because the tumor cells can move between individual fish, the discovery challenges previous understandings of how cancer behaves in aquatic environments.
The study, published in 2026 [2], was led by fish disease specialists from the University of Vermont and Université du Québec [1]. The affected fish are brown bullhead catfish living in Lake Memphremagog, a body of water that straddles the border between Vermont and Quebec [1].
According to the research, this specific cancer has been present in the lake population for more than 10 years [3]. While most cancers develop from a mutation in an individual's own cells, transmissible cancers involve cells from one animal being grafted onto another. This case represents only the fourth known example of such a phenomenon in the animal kingdom [4].
Health officials have addressed concerns regarding the impact on people. Some reports indicate that Quebec's Ministry of the Environment recommends against eating fish with tumors [5]. However, other officials said there is currently no evidence that the cancer poses a risk to humans and no formal advisory has been issued [3].
The research team utilized genomic analysis to confirm that the tumors were melanoma-like and capable of transmission. The persistence of the disease for over 10 years [3] suggests a stable transmission cycle within the lake's ecosystem. Scientists are now working to understand how the cancer spreads and whether it affects other fish species in the region [1].
“the first known case of a contagious cancer in a freshwater species”
The discovery of transmissible cancer in freshwater fish expands the known scope of contagious malignancies, which were previously rare and limited to a few species. This suggests that the mechanism for cellular transmission is more versatile than previously thought, potentially alerting ecologists to hidden threats in other freshwater biodiversity hotspots.
