Full Breakdown
Transmissible Melanoma Identified in Brown Bullhead Catfish of Lake Memphremagog
7/29/2026, 10:45:26 AM
Discovery of a Novel Cancer in Freshwater Fish
Scientists from the University of Vermont and the state Fish and Wildlife department examined brown bullhead catfish (Ameiurus nebulosus) from Lake Memphremagog, a cross-border lake shared by Vermont and Quebec. Biologists noted dark, tar-like lesions on the skin, gills, lips and eyes of the fish. Laboratory analysis confirmed the lesions were melanoma, and genomic sequencing showed the tumor cells were clonally related across different hosts—evidence of a transmissible cancer. The findings were published in *Nature* and represent the first documented case of a transmissible cancer in a freshwater fish species, adding a fourth type of transmissible cancer to the animal kingdom.
Prevalence and Genetic Signature
Sampling conducted from 2012 through 2014 revealed that 23 % to 37 % of the examined catfish carried melanoma lesions, with nearly one in three fish affected by 2014. Co-lead researchers Julie Dragon and Mark Henderson described the cancer cells as behaving more like parasites than typical tumors.
Environmental Factors Under Investigation
Researchers hypothesize that the outbreak may be linked to environmental stressors. The team observed elevated arsenic levels in tumor cells and noted a geographic correlation between cancer incidence and arsenic concentrations in surrounding soils. They also cited the 2011 flooding from Hurricane Irene, which introduced runoff pollutants and reduced water quality, as a possible catalyst for immune suppression in the fish population.
Implications and Ongoing Research
The discovery raises questions about the broader potential for transmissible cancers in wildlife and, theoretically, in humans. While the American Cancer Society reiterates that cancer transmission between humans is not possible, the study underscores how cancer cells can survive outside their original host. Researchers are expanding surveys to ponds and rivers in Massachusetts and other New England lakes to assess the distribution of the disease and to determine whether similar cancers have been overlooked.
Verbatim Quotes
- “At first, we thought this disease might be a virus, but that wasn’t panning out,” — Julie Dragon
- “Arsenic is found naturally throughout New England, and there’s really high concentrations of it in the Vermont’s Northeast Kingdom as well as up through Maine, which is where we’ve also seen evidence of this cancer,” — Henderson. The, researcher
- “Our contention is that maybe it’s not as rare as everyone thinks. We’re just not seeing it,” — Julie Dragon
