Researchers announced on July 26, 2026 that a melanoma‑type transmissible cancer has been found in brown bullhead catfish inhabiting Lake Memphremagog, a body of water that straddles the border between Quebec and Vermont. Examination of fish from the lake revealed that about one third of the specimens tested carried the disease, marking the first documented instance of a transmissible cancer in a fish species.
The condition, identified as a melanoma‑type tumor that can spread between individual catfish, represents a novel health challenge for the lake's aquatic ecosystem. While the precise mechanisms of transmission were not detailed in the initial report, the finding confirms that the cancer can move from one host to another, a behavior previously observed only in a limited number of mammalian cancers.
Transmissible cancers are considered exceptionally rare in nature. Prior to this discovery, such diseases had been recorded in only a few mammal species, including certain Tasmanian devils and dogs. The emergence of a similar phenomenon in fish expands the known range of organisms capable of supporting cancer cells that can survive outside their original host and establish new tumors in separate individuals.
The researchers emphasized the significance of the discovery for both wildlife health monitoring and broader scientific understanding of cancer biology. By documenting a transmissible tumor in a non‑mammalian vertebrate, the study provides a new model for investigating how cancer cells adapt to different host environments and how they might be controlled in natural populations. Ongoing surveillance of Lake Memphremagog's catfish populations will be necessary to assess the spread of the disease and its impact on the lake's ecological balance.