American researchers have identified a contagious form of melanoma spreading among dwarf catfish in freshwater lakes across the northern United States and southern Canada. The study revealed that in certain bodies of water, tumorous growths were found in approximately one-third of the local fish population. The discovery was announced by the press office of the University of Vermont (UVM).
The work was conducted as part of a biological survey of lakes in Vermont and neighboring regions of the U.S. and Canada. Starting in 2012, residents and naturalists began reporting an unusually high frequency of melanoma in caught catfish, despite these bottom-dwelling fish being rarely exposed to sunlight. Scientists decided to investigate the causes of the tumors and examined several dozen fish caught in areas along the border between Vermont and the Canadian province of Quebec.
Researchers extracted the growths from the catfish and analyzed their structure and genetic composition. It turned out that cancer cells from different individuals contained an identical set of mutations, indicating a single source of origin for the tumors. Furthermore, the DNA of these cells differed significantly from the fish’s own genome and contained hundreds of thousands of mutations absent in the healthy tissues of the catfish.
The findings suggest that the tumor cells multiplied over an extended period and managed to spread between different individuals. Scientists believe this is a contagious form of cancer that transmits from one fish to another. The exact mechanism of melanoma transmission has not yet been determined, but it is suspected that infection may occur during spawning, as nearly all tumors were found in adult specimens.
Julia Dragon, an associate professor at the University of Vermont, noted that the discovery highlights the potential for widespread contagious cancers in nature, which may have previously gone unnoticed due to a lack of targeted research. Studying such tumors, she said, will help better understand how cancer cells leave their original host and retain the ability to thrive in new environments.
In the future, scientists plan to continue monitoring infected catfish to determine their lifespan, the disease’s impact on population numbers, and possible consequences for ecosystems. Researchers also intend to investigate whether this form of contagious cancer poses any threat to humans.
Contagious types of cancer have previously been observed in various animals. These include CTVT, a disease affecting dogs that has existed for around 10,000 years, as well as two forms of DFTD in Tasmanian devils, whose spread has led to population declines in these animals. Additionally, about ten varieties of transmissible tumors have been found in mollusks, some of which are capable of infecting different species of invertebrates.
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