Contagious Skin Cancer Discovered in Freshwater Fish for the First Time

Researchers have discovered the first known contagious cancer in fish—a transmissible melanoma affecting brown bullhead catfish in Lake Memphremagog, which spans Quebec and Vermont. The cancer, which appears as black, tar-like lesions, has infected roughly a third of the catfish population in the lake and has also been found in other New England water bodies, according to a study published in Nature.

The Discovery

The lesions were first noticed by anglers and state biologists around 2012-2013. Initially suspected to be caused by a virus or pollutant, genomic analysis revealed the tumors were genetically distinct from their hosts but nearly identical to each other, indicating they arose from a single ancestral cancer that spread like an infectious agent. "These tumors were very different from the host fish that they came from, which is not what we expected," said Julie Dragon, a co-author at the University of Vermont Source: NPR.

Cause and Spread

Unlike typical melanomas in humans caused by UV exposure, these catfish are bottom-dwellers with minimal sun exposure. The cancer cells appear capable of surviving in the aquatic environment and infecting new fish. "Those cells can somehow escape the host, maybe live in the environment—the aquatic environment—and then infect a new host," Dragon explained Source: Gizmodo. This makes it only the fourth known type of transmissible cancer in animals, alongside contagious cancers in dogs, Tasmanian devils, and some bivalves Source: Gizmodo.

Implications

Researchers emphasize that the discovery raises many questions about how these cells evade immune systems and establish new infections, potentially offering insights into metastasis in humans. The study is published in Nature on Wednesday Source: Ground News.