Overview
- A study published July 22 in Nature used whole‑genome sequencing to show tumor cells from multiple brown bullhead catfish form a single clonal lineage distinct from their hosts, supporting transmission of cancer cells between fish.
- Researchers first noticed unusually high melanoma rates in Lake Memphremagog beginning in 2012–2013 and earlier sampling found about 23–37 percent of fish in affected collections had confirmed melanomas.
- Genetic screens found no virus or bacterium uniquely tied to the tumors, which supports the view that the cancer cells themselves are the transmissible agent.
- Tumor tissue showed elevated arsenic and the cancer overlaps areas with natural arsenic, but scientists stress this is a correlation not proof of cause and are running controlled tests to check environmental roles.
- Teams are now mapping the lineage’s geographic spread, running lab transmission experiments focused on spawning contact and environmental exposure, and advising caution such as avoiding visibly tumored fish while saying there is no evidence of risk to humans.