Scientists Find 1st Contagious Fish Cancer After Lesions Hit 1 in 3 Catfish

3 articles · Updated · Gizmodo · Jul 22

Nature researchers traced black skin lesions in brown bullhead catfish to a transmissible melanoma, the first contagious cancer ever documented in fish and only the fourth known in animals.
Genetic sequencing of Lake Memphremagog tumors found hundreds of thousands of shared variants absent from the host fish, showing the cancer cells are spreading between animals rather than arising independently.
By 2014, roughly a third of catfish in the area had lesions; the disease has since been detected in other New England lakes and ponds, including sites without major pollution sources.
Scientists still do not know how the cancer spreads or how deadly it is, though spawning-season contact, lake-bottom survival of cancer cells, and arsenic-linked vulnerability are leading hypotheses.
The finding makes this the first transmissible cancer in a freshwater animal and suggests similar parasite-like cancers may be more widespread than researchers have recognized.