First-known freshwater contagious cancer spreading among catfish in Vermont lake - FOX Weather

What the report says

Fox Weather reported that scientists have identified what is believed to be the first known contagious cancer documented in a freshwater fish population, affecting brown bullhead catfish in Lake Memphremagog, a glacial lake spanning Vermont and Quebec. The finding comes from a study published in Nature, after researchers investigated unusually frequent raised black lesions seen in the fish since 2012.

According to the report, the lesions were determined to be malignant melanomas. Sampling between 2014 and 2017 found the tumors in 23% to 37% of brown bullheads examined. Because the lake is used as a drinking-water source for about 175,000 people, researchers examined whether the cancer might be linked to environmental contamination or an infectious process. One possible factor considered was runoff and reduced water quality after Tropical Storm Irene caused major flooding in 2011, though the article does not report that this was established as the cause.

Researchers used genomic analyses comparing healthy tissue, normal tissue from affected fish and tumor samples from lesions at varying stages. Fox Weather reported that the tumor genomes were more similar to one another than to the DNA of their individual hosts, evidence consistent with a single clonal cancer moving between animals rather than tumors arising independently in each fish.

The finding is significant because transmissible cancers are rare and previously had been documented in only a small number of animal groups, including dogs, Tasmanian devils and several bivalves. The study has not determined exactly how the cancer spreads among brown bullheads, though researchers suggested future sampling could help clarify its origin, age, transmission route and impact on the local fish population.