Anglers had been reporting black skin patches among catfish in Vermont lake. Now scientists have found it - The Times of India

What the report says

The Times of India reported on July 28, 2026, that scientists studying brown bullhead catfish in Lake Memphremagog, a lake shared by Vermont and Quebec, have identified the black raised skin patches long noted by anglers and biologists as a transmissible melanoma. The report said the finding, published in Nature, makes catfish only the fourth known example in nature of a contagious cancer, after cases documented in Tasmanian devils, dogs and shellfish.

According to the report, sightings of affected fish increased from around 2012, and by 2014 about 30% of sampled bullheads showed the dark lesions. Researchers initially considered causes such as a virus, pollution-related disease or another pathogen, partly because brown bullheads are often used as indicators of environmental conditions. Whole-genome sequencing later showed that tumor cells from different fish were more closely related to each other than to the fish carrying them, a genetic pattern consistent with a single cancer cell lineage moving between hosts.

The mechanism of spread remains unresolved. The Times of India said researchers are considering whether the cancer moves during spawning, when fish cluster in shallow water, or through contact with water or sediment that may contain cancer cells. Naturally occurring arsenic was also mentioned as a possible factor under study, but not established as a cause.

The report said the long-term ecological effect is not yet known, although some heavily diseased fish can live for years. Lake Memphremagog supplies drinking water to more than 175,000 people, but researchers cited in the article said there is no known human risk. Sampling has found the cancer in a few other regional lakes and ponds, with further surveys underway.