Transmissible melanoma discovered in Vermont’s Lake Memphremagog catfish

Scientists from the University of Vermont have identified a rare transmissible skin melanoma in brown bullhead catfish living in Lake Memphremagog, a body of water that spans the border between Vermont and Quebec. Anglers first noted the dark, raised lesions on the fish in 2012, and surveys by 2014 showed that roughly one‑third of the sampled catfish carried the tumors.

Whole‑genome sequencing revealed that tumor cells from different fish are far more genetically alike to each other than to their host fish, confirming a clonal cancer that passes directly from one animal to another. This is only the fourth naturally occurring transmissible cancer recorded, following similar diseases in dogs, Tasmanian devils and marine bivalves. While the disease does not appear to pose a direct threat to human health, its prevalence in a key indicator species raises concerns about environmental stability and water‑quality management. Researchers are now investigating the cancer’s origin and pathways of spread.