Scary Finding in Catfish: a Contagious Cancer

Researchers on a Vermont-Quebec border lake have stumbled onto something never seen in fish before: a cancer that appears to spread like an infection. The ailment is affecting brown bullhead catfish in Lake Memphremagog, reports the New York Times. For more than a decade, the fish have been turning up with black growths and lesions on their bodies that were eventually found to be melanomas, or skin cancer, notes NPR. That's rare enough. Now, a new study in Nature suggests that the cancer traces back to a single fish that developed a tumor and shed cancer cells into the lake.

"It is the infectious agent itself," says study co-author Julie Dragon of the University of Vermont. "Those cells can somehow escape the host, maybe live in the environment—the aquatic environment—and then infect a new host." The finding adds catfish to a short list of animals known to host transmissible cancers, alongside dogs, Tasmanian devils, and some shellfish and clams. Researchers suspect close-contact spawning and bites give the cancer cells an entry point, and they're now hunting for cases elsewhere. As Dragon puts it: "Is this really as rare as we think it is, or are we just not looking?" They're also urging anglers not to eat tumor-covered fish, while stressing there's no evidence the disease can infect humans.