Contagious Melanoma Discovered in Freshwater Fish for First Time

Scientists have identified the first contagious cancer in a freshwater fish species—a melanoma that spreads between brown bullhead catfish in Lake Memphremagog. The cancer, which manifests as black skin lesions, was first noticed in 2012 and by 2014 nearly one in three fish was affected Source: abc.es.

The Discovery

Researchers at the University of Vermont sequenced the genomes of tumors and healthy tissue. They found tumor cells were more genetically similar to each other than to their host fish, confirming a clonally transmissible cancer Source: infobae. This is only the fourth known transmissible cancer in animals, after Tasmanian devil facial tumor disease, canine venereal tumor, and leukemia-like diseases in bivalves Source: elmundo.es.

How It Spreads

The cancer appears limited to large, reproductively active fish. During spawning, catfish gather densely in shallow water, allowing physical contact that may transfer tumor cells Source: abc.es. The fish are scaleless bottom-dwellers, and sediment could harbor free-floating cancer cells Source: diariolibre. Contaminants or hormonal changes may weaken immune systems, making fish more vulnerable Source: infobae.

No Risk to Humans

Researchers emphasize the cancer poses no known threat to humans Source: elmundo.es. The ecological impact remains uncertain; some transmissible cancers are devastating (Tasmanian devil), while others (canine tumor) coexist for millennia. The study appears in .