Scientists Discover The Fourth Transmissible Cancer Known To Science - Forbes

What the report says

Forbes reported that researchers at the University of Vermont have identified a contagious melanoma spreading among brown bullhead catfish in Lake Memphremagog, a lake that crosses the Vermont-Quebec border. The finding, published this week in Nature, is described as the fourth known type of transmissible cancer, the first documented in a fish and the first found in freshwater.

According to Forbes, the disease was first noticed in 2012 when an angler brought an unusually darkened bullhead to Vermont Fish and Wildlife biologist Peter Emerson. Within several years, black growths were appearing on roughly a quarter to 40% of the lake’s bullhead. Researchers initially looked for environmental pollutants, viruses or microbes, but sequencing did not identify an infectious organism or chemical pattern that explained the tumors.

The key evidence came from genetic comparisons led by University of Vermont microbiologist Julie Dragon’s team. Forbes reported that the tumors grouped genetically with each other rather than with the individual fish carrying them, indicating the cancer cells themselves were moving between animals. The article says similar tumors have since been detected across parts of the northeastern United States and Canada, though Emerson noted that in his Vermont district the cancer has appeared in only one of about 90 lakes.

The discovery matters because transmissible cancers are considered unusual and difficult to detect in wildlife without paired tumor-and-host genomic testing. Forbes noted comparisons with known transmissible cancers in Tasmanian devils and bivalves, while researchers suggested more cases may be overlooked. The bullhead population in Lake Memphremagog remains abundant, but the disease could affect feeding structures such as barbels and may offer new insight into how cancers spread in natural ecosystems.