A new scientific study published in Nature has identified the fourth known contagious cancer globally, marking the first time a transmissible tumor has been documented in freshwater fish.
Scientists examining wild populations in a cross-border lake have documented a rare and unusual biological phenomenon: a cancer that acts as an infectious disease.
From a Single Catch in Lake Memphremagog to an Epidemic Spread
The discovery traces back to 2012, when a fisherman hauled in a brown bullhead catfish bearing tar-like black patches from Lake Memphremagog, sitting between the American state of Vermont and the Canadian province of Quebec. Over a span of just three years, those melanoma tumors expanded to strike between 25% and 40% of the lake’s catfish population, prompting intensive genetic analysis and wide-scale surveys.
Researchers determined that the examined tumors share identical genetic mutations, forming a unified hereditary mass entirely separate from the host fish’s own healthy tissue. Field surveys revealed that the condition marched across the 30-mile-long transboundary lake within five years of its initial appearance. Similar cases have since been flagged in other American states and Canadian provinces, including Maine, Massachusetts, Pennsylvania, Wisconsin, and New York.
Understanding a Clonal Cancer and Its Impact on Catfish Populations
Peter Emerson, a fisheries biologist with the Vermont Fish and Wildlife Department, noted that the rapid transmission increasingly resembles an outbreak. Growths materialize across the external surfaces of the fish, inside their mouths, and along their sensory barbels, ultimately impairing their ability to feed.
The spread of the disease now looks like an epidemic. Peter Emerson, fisheries biologist with the Vermont Fish and Wildlife Department
Human Activity and the Puzzle of New Waterways
Unlike typical cancers arising from internal genetic mutations or environmental toxins, this freshwater fish affliction relies on horizontal cell transmission without bacterial or viral triggers. Scientists investigating the geographic spread strongly suspect that human activity plays a central role in transporting these malignant cells into fresh bodies of water.
