A recent genetic study has found that melanoma tumors are spreading among catfish populations in Quebec and the northeastern U.S., marking the first instance of transmissible cancer in fish and one of only a few cases ever documented. Julie Dragon, a lead researcher on the study, highlighted the rarity of such occurrences in nature, with only three other transmissible cancers previously identified in Tasmanian devils, dogs, and shellfish.
The discovery of melanoma skin cancer tumors in brown bullhead catfish in Lake Memphremagog, following reports from anglers in 2012, raised concerns among locals about potential carcinogenic contamination in the water. Approximately one-third of the catfish in the lake now exhibit these tumors, with varying degrees of severity and spread to other organs.
Despite initial suspicions of environmental factors, tests for carcinogens in the lake have not yielded definitive results. In 2014, Julie Dragon’s team investigated the possibility of a viral cause for the tumors but found no evidence of viral involvement. Subsequent genetic testing revealed surprising results, showing that the cancer cells in the fish were more similar to each other than to their host cells, suggesting a transmissible nature.
The transmission of the tumors among adult catfish is hypothesized to occur during spawning when the fish come into contact with each other. While researchers have not yet demonstrated direct transmission between fish, ongoing studies aim to clarify this aspect. Some scientists remain cautious about labeling the cancer as transmissible until direct transmission is proven.
Funding for the study was provided by various U.S. and Vermont government agencies, with support from Quebec’s Ministry of the Environment. Recommendations from the Ministry advise against consuming fish with tumors, although there is no evidence of harm to human health. Instances of catfish with tumors have been reported in other lakes, prompting efforts to track and monitor affected populations for further research.
