A groundbreaking genetic study indicates an unusual occurrence of melanoma tumors spreading among catfish populations in Quebec and the northeastern U.S. This discovery marks the first documented instance of transmissible cancer in fish, a rare phenomenon previously observed only in Tasmanian devils, dogs, and shellfish.
The investigation began when anglers in Lake Memphremagog reported catching brown bullhead catfish with peculiar black spots and lumps in 2012, later confirmed as melanoma skin cancer tumors. Subsequently, about one-third of the lake’s brown bullheads have developed these tumors. While the extent of the fish’s illness varies, some cases show cancer spreading to vital organs like the brain or liver, though many fish with lesions appear healthy, indicating they can coexist with the disease.
Following concerns about potential carcinogens in the lake after a significant flood post-tropical storm Irene, tests for such substances yielded inconclusive results. In response, Julie Dragon, an associate professor at the University of Vermont, investigated the potential role of a virus in the fish tumors in 2014.
Genetic analyses revealed surprising findings: despite a diverse genetic makeup, the cancer cells bore greater resemblance to each other than to their host fish. Collaborating with other experts, the researchers speculated on the transmission mechanism, considering the possibility of the disease being sexually transmitted during spawning.
While the transmission of tumors between fish has not been conclusively demonstrated, ongoing research aims to validate this hypothesis. Some scientists remain cautious, awaiting further evidence to confirm the transmissible nature of the cancer. Notably, the study was funded by various government agencies and supported by Quebec’s Ministry of the Environment, which advises against consuming fish with tumors as a precaution, despite lacking evidence of harm to human health.
