Scientists have identified the first known transmissible cancer in freshwater fish, specifically in brown catfish inhabiting Lake Memphremagog, which spans Vermont and Quebec.

The discovery, published in Nature, reveals that the melanomas in these fish share a common genetic origin, suggesting cancer cells themselves may spread between individuals.

Researchers initially suspected environmental pollutants or pathogens due to the high incidence of tumors (23-37% of specimens), but genetic analysis showed tumors from different fish shared unique mutations, unlike human melanomas.This indicates the cancer may spread through physical contact during spawning, waterborne transmission, or hormonal changes affecting immunity.

While arsenic levels in tumors correlate with the lake's geology, the study emphasizes the cancer's cellular origin rather than external factors.

The findings could advance cancer research by studying how tumors survive outside their host, offering insights into cancer containment and metastasis.Researchers advise against consuming infected fish due to potential health risks.