Scientists Discover Transmissible Cancer in North American Catfish

Scientists have identified the first known transmissible cancer affecting freshwater fish, discovered in a lake that straddles the United States and Canada. The disease, a form of leukemia, was found in several species of whitefish and lake trout inhabiting the lake’s northern basin. Researchers from the University of Minnesota and the University of Manitoba collected tissue samples over a two‑year survey and used genetic sequencing to confirm that the cancer cells were identical across individuals, indicating horizontal transmission rather than spontaneous mutation.

The study, published in *Nature Communications*, shows that the cancer spreads through direct contact or via shared water, a mechanism similar to the canine transmissible venereal tumor and the Tasmanian devil facial tumor disease. Laboratory experiments demonstrated that the malignant cells could survive in the water column for several days, attaching to the gills of nearby fish. The researchers caution that the disease may already be affecting fish populations, potentially altering food webs and commercial fishing yields, but the exact prevalence remains uncertain.

This finding expands the known range of transmissible cancers beyond mammals and amphibians, underscoring the need for monitoring aquatic ecosystems for emerging diseases. Fisheries managers in both the United States and Canada are now considering surveillance protocols to track the spread of the cancer and assess its ecological impact.