Transmissible melanoma identified in brown bullhead catfish in Lake Memphremagog

Scientists have identified a transmissible form of melanoma affecting brown bullhead catfish in Lake Memphremagog, a glacial lake that spans Vermont and Quebec. The disease was first noted in 2012 when a high incidence of raised black lesions was observed on the fish. Sampling between 2014 and 2017 revealed that 23% to 37% of the catfish examined carried malignant melanomas.

Genomic analyses showed that tumor tissue differed markedly from healthy tissue and that tumor genomes from different fish were more similar to each other than to the host DNA, indicating a single clonal origin. The findings suggest the cancer spreads between individuals, making it the first documented transmissible cancer in a freshwater fish species.

The researchers considered environmental factors, including runoff after Tropical Storm Irene in 2011, but the exact transmission mechanism remains unclear. They hypothesize that the disease may be passed through reproductive processes or age-related factors, similar to other known transmissible cancers in dogs, Tasmanian devils and certain bivalves.

"Future sampling of affected populations will help determine the age and origin of this clonal cancer and its impact on brown bullhead numbers," the study authors said.

Lake Memphremagog supplies drinking water to about 175,000 people, prompting ongoing monitoring to assess any broader ecological or public-health implications.