Contagious Cancer Found in North American Catfish - WIRED

What the report says

Wired reports that an international research team has identified a transmissible melanoma in brown catfish in Lake Memphremagog, which lies across Vermont and Quebec. The finding, published this month in Nature, is described as the first known contagious cancer in fish and the first recorded in a freshwater ecosystem.

The investigation began after fishermen and biologists noticed many catfish with dark lesions in the lake in 2012. Earlier work found the marks were malignant melanomas, with tumors seen in roughly 23% to 37% of examined fish. Researchers initially considered explanations such as pollution, a pathogen or degraded water quality after Tropical Storm Irene, especially because the lake is also a drinking-water source for more than 175,000 people.

According to Wired, genome sequencing of tumors and healthy tissue pointed to a different explanation: tumors from separate fish were genetically closer to one another than to their own hosts. The cancers shared many genetic variants that were not present in the fish’s healthy cells, a pattern the researchers considered consistent with a single cancer lineage spreading between animals. The team did not find a virus or bacterium specifically linked to the tumors, though it did not fully exclude a possible role for pathogens in the cancer’s origin or spread.

How the disease moves between catfish remains unresolved. Researchers suggested close contact during spawning, temporary survival of cancer cells in water or sediment, or reproductive immune changes as possible factors. They also noted an association with naturally high arsenic areas, while cautioning that this does not prove causation.