Scientists Just Discovered a Contagious Cancer in a Catfish, the Fourth Known to Science. Meet the Other Three

Scientists reported a contagious melanoma in a brown bullhead catfish, the first known transmissible cancer in a fish.

It becomes the fourth known cancer that can spread between animals, alongside cases in dogs, Tasmanian devils, and soft-shell clams.

The discovery broadens understanding of how rare tumor lineages survive, spread, and evade immune defenses.

Researchers say the finding could shed light on cancer biology across species and how transmissible tumors persist.