In July 2026, researchers announced the identification of a transmissible melanoma cancer affecting brown bullhead catfish in Lake Memphremagog, which straddles the Quebec‑Vermont border. Laboratory analysis indicated that roughly one‑third of the sampled bullheads carried melanoma tumors that can spread between individuals.
The disease was detected during routine health surveys of the lake’s fish populations. Tissue samples from affected catfish revealed malignant cells consistent with melanoma that were capable of moving from one fish to another, a mode of transmission previously unrecorded in fish. The findings mark the first documented instance of a transmissible cancer in any fish species.
Transmissible cancers are known in a limited number of mammals, such as the Tasmanian devil facial tumor disease and the canine transmissible venereal tumor. Their occurrence in vertebrates is considered exceptionally rare, and the new catfish case expands the range of hosts to aquatic environments. Researchers emphasized that the presence of a transmissible melanoma in a widely distributed freshwater species could have implications for ecosystem health and fisheries management.
Lake Memphremagog, a deep glacial lake covering parts of southern Quebec and northern Vermont, supports diverse fish communities, including the brown bullhead, a catfish commonly found in North American freshwater bodies. The detection of cancer in a substantial portion of this population raises questions about potential environmental factors that may facilitate disease spread, although no causal links have been established.
Ongoing monitoring will aim to determine the prevalence of the tumor over time and assess any impact on the lake’s ecological balance. The research team plans to continue sampling across seasons and to compare findings with other regional water bodies to evaluate whether the transmissible melanoma is confined to Lake Memphremagog or appears elsewhere.