Researchers in Vermont have identified a contagious form of cancer affecting brown bullhead catfish in Lake Memphremagog, marking the first known case of a transmissible cancer in fish and the fourth overall in animals.

The study, published in Nature, found that melanoma tumors from affected catfish share unique genetic variants not present in their hosts, indicating the cancer spreads like an infectious disease.This discovery challenges the rarity of transmissible cancers, which are typically unexpected in nature.The cancer's spread across New England lakes, despite no major pollution sources, suggests it may have evolved into a parasite-like entity.

Scientists remain puzzled about transmission methods, potential environmental factors like arsenic exposure, and the cancer's impact on catfish populations.

While not a threat to humans, the findings highlight the need for further research into how cancers evade immune systems and the broader implications for cancer biology.