Genetic testing of melanoma tumors in catfish from lakes across Quebec and the northeastern United States has revealed that the skin‑cancer cells can move from one fish to another. The study, released on July 22, 2026, indicates that the malignant growths are not confined to a single host but can be transmitted through the water, a phenomenon previously considered exceptionally uncommon in wildlife.
Researchers examined the DNA of melanoma tumors taken from multiple catfish populations and found a close genetic match that could only be explained by direct spread rather than independent development. The analysis showed that the cancerous cells shared identical mutations, suggesting a common origin that moved between individual fish sharing the same aquatic environment.
The discovery adds to a short list of known transmissible cancers, which includes a few documented cases in mammals and marine life. In those instances, cancer cells themselves act as a parasite, evading the host’s immune defenses. The catfish findings represent the first indication that a melanoma‑type skin cancer may behave similarly.
While the occurrence appears limited to certain lakes in the region, scientists caution that the rarity of such events makes it difficult to predict broader ecological impacts. Ongoing monitoring of catfish health and further genetic sampling are planned to determine whether the transmissible melanoma is spreading, remains isolated, or poses a risk to other species.
The research underscores the importance of genetic surveillance in wildlife disease studies, offering a new perspective on how cancers can cross individual boundaries. By documenting a possible case of contagious melanoma in fish, the work expands understanding of cancer biology and may inform future investigations into disease dynamics in aquatic ecosystems.