Scientists have identified what appears to be the fourth transmissible cancer ever documented and the first known case in a fish. The disease is a melanoma whose cancer cells spread between brown bullhead catfish living in Lake Memphremagog in Vermont.
The finding traces back to 2012, when an angler caught a brown bullhead with a dark growth that looked like tar smeared across the fish. That unusual case helped launch a closer investigation into whether the tumors were arising separately in individual fish or moving from one animal to another.
Researchers concluded that the melanoma is transmissible, meaning the cancer itself is passed between fish through living tumor cells rather than developing independently each time. That makes the discovery especially notable, because transmissible cancers are considered extremely rare in nature.
The report expands scientific understanding of how cancer can behave outside the usual pattern of disease within a single body. It also adds a new animal group to the very short list of species known to experience cancers that can spread directly between individuals.
