Researchers have identified a rare, transmissible cancer affecting brown bullhead catfish in Lake Memphremagog on the U.S.-Canada border. First observed in 2012, the malignant melanoma spreads between individual fish, a phenomenon rarely seen in the animal kingdom. Experts advise anglers to avoid consuming fish showing visible skin lesions as a precautionary measure.
Melanoma Outbreak in Lake Memphremagog
The discovery of transmissible cancer in brown bullhead catfish (Ameiurus nebulosus) has drawn significant scientific attention to Lake Memphremagog, which spans the border between Vermont and Quebec. By the period between 2014 and 2017, the prevalence of these malignant melanomas had reached a significant portion of the local population.
While the disease has since been identified in other locations, the incidence rates outside of this primary site remain significantly lower. The findings, published in the journal Nature, characterize this as a novel form of contagious cancer, where tumor cells from one animal are capable of inducing lesions in another.
Biological Transmission and Environmental Factors
Transmissible cancers are exceptionally rare in the natural world. Better-known examples include the facial tumor disease affecting Tasmanian devils and the canine transmissible venereal tumor (CTTV). The mechanism behind the spread among the bullhead catfish is currently under investigation by researchers, who are examining how these malignant cells survive and propagate between hosts.
Current hypotheses suggest that the fish may transmit the cancer during the spawning season. Potential vectors for this spread include direct physical contact or transmission through the water. Researchers are also exploring whether environmental stressors that weaken the fish’s immune systems—or hormonal changes related to reproduction—render the animals more susceptible to the disease.
Public Health Recommendations for Anglers
While there is currently no evidence suggesting that this specific type of melanoma poses a risk to humans, health authorities and researchers are maintaining a stance of caution. The primary recommendation for those fishing in the affected waters is to avoid the consumption of any fish that displays visible lesions or abnormal skin growths.
Ongoing efforts are focused on determining the evolutionary origin of the cancer and identifying exactly when it first emerged. By studying the lineage of these cells, scientists hope to better understand the broader patterns of transmissible neoplasia that have been observed in other aquatic species, including various bivalves, as documented in the Nature research data.
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