A recent genetic study suggests an unusual case of melanoma tumours spreading among catfish in Quebec and the northeastern U.S., marking the first known transmissible cancer in fish. According to the study published in the journal Nature, only a few transmissible cancers have been identified previously, including in Tasmanian devils, dogs, and shellfish.
The discovery of melanoma skin cancer tumours in brown bullhead catfish in Lake Memphremagog, reported by anglers in 2012, raised concerns. Approximately one-third of the brown bullheads in the lake now have these tumours, with some cases showing spread to other organs like the brain or liver. Despite the lesions, many fish appear healthy, suggesting they can live with the disease for a period.
Following a huge flood caused by post-tropical storm Irene in 2011, locals feared the tumours were linked to carcinogens washed into the lake by floodwaters. Although tests for carcinogens yielded inconclusive results, a study found elevated metal concentrations in the skin of fish with tumours.
Investigating a potential viral cause, Julie Dragon, a microbiology and molecular genetics professor, conducted genetic tests on both healthy and infected fish. Surprisingly, the cancer cells on the fish were more similar to each other than to the host’s cells, indicating a unique situation.
Speculations arise about the transmission of these tumours during spawning, where adult fish cluster together, potentially allowing cell transfer. While no direct transmission has been demonstrated yet, ongoing research aims to confirm this possibility.
Despite differing opinions among scientists, ongoing studies funded by various government agencies aim to understand the spread and impact of these transmissible tumours. Recommendations advise against consuming fish with tumours, although there is no evidence of harm to human health. Monitoring efforts in various lakes aim to track the prevalence and impact of these unique cancer cases among catfish populations.
