A contagious cancer discovered in catfish: a scientific first

Researchers have identified a transmissible melanoma in the brown bullhead, a species of freshwater catfish. Observed since 2012 in Lake Memphremagog, on the border between the United States and Canada, the tumors appear as black lesions on the skin. Between 2014 and 2017, they affected 23 to 37% of the fish studied.

Genetic sequencing revealed that tumors taken from different fish were more similar to each other than to tissues from their own hosts. The cancer cells therefore appear to originate from a single lineage capable of passing from one animal to another and developing as a parasite. This is the first transmissible cancer identified in a fish and in a freshwater environment. Study published in "Nature"

The mode of transmission remains a mystery.

Scientists still don't know exactly how the cells spread between fish. Close contact during reproduction or the presence of tumor cells in the water are among the hypotheses being investigated, but none have been definitively proven. Unlike the disease that is decimating Tasmanian devils, this melanoma does not appear to cause significant excess mortality in catfish.

There is no evidence to suggest that this cancer can infect humans, other animals, or drinking water. Researchers are nevertheless continuing their work to establish its origin, measure its long-term impact on fish populations, and determine whether environmental changes have facilitated its emergence. Above all, the discovery broadens our understanding of these exceptionally rare cancers, previously observed only in dogs, Tasmanian devils, and certain shellfish.