Contagious Skin Cancer Discovered in Catfish of Lake Memphremagog

A study published in Nature on July 22 reveals that brown bullhead catfish in Lake Memphremagog, straddling Vermont and Quebec, are afflicted with a contagious form of melanoma. Roughly one-third of the lake's bullheads carry the lesions, which appear as black tar-like blotches. Genetic analysis by Julie Dragon at the University of Vermont showed that all tumor cells are near-identical clones, distinct from the host fish, indicating a single ancestral cancer cell that has been spreading between individuals for years. This is the first documented transmissible cancer in a fish species and the first known to spread in fresh water. The cancer likely spreads during spawning season when fish crowd together and scratch each other with sharp spines. Some researchers, including Vicki Blazer formerly of the U.S. Geological Survey, dispute the conclusion, suggesting environmental toxins like arsenic may be the primary cause. Elizabeth Murchison of the University of Cambridge supports the transmissible cancer theory, calling the genetics conclusive. The discovery challenges assumptions about cancer transmission, as cells typically require salty fluids to survive.