Researchers Identify First Likely Transmissible Cancer in Wild Catfish

Scientists studying brown bullhead catfish in Lake Memphremagog, which borders Vermont and Quebec, reported that 23% to 37% of sampled fish carried melanoma lesions, a rate far higher than previously recorded. Whole-genome sequencing showed that the tumor DNA from multiple fish was nearly identical and distinct from the host fish DNA, indicating the tumors likely originated from a single lineage of cancer cells that have been passed between individuals. The researchers noted that the exact mechanism of transmission remains unknown, though close contact during spawning season may provide opportunities for cell transfer.

"The tumors appear to have come from a single line of cancer cells that have then spread from fish to fish, rather than occurring independently," the study authors wrote.

The finding represents the first documented case of a transmissible cancer in a freshwater environment and adds fish to the short list of species—such as dogs, Tasmanian devils, and certain bivalves—known to host naturally spreading cancers. While Lake Memphremagog supplies drinking water to over 175,000 people, the researchers emphasized that there is no evidence the catfish cancer can infect humans or other species.

The discovery may provide new insights into how cancer cells evade immune defenses and persist in new hosts, potentially informing broader cancer research.