Transmissible Melanoma in Catfish

Published by

The AquaRepto Hobbyist

Researchers identified a transmissible melanoma in brown bullhead catfish (Ameiurus nebulosus). The tumors appear as black, sometimes crusty lesions on the skin. In severe cases, the melanoma spreads internally to the brain and liver. Consequently, this marks the first confirmed case of naturally contagious cancer in any fish species.

Where Was This Transmissible Melanoma in Catfish First Detected?

Anglers first spotted the strange black lesions in 2012 at Lake Memphremagog. This lake stretches across the border between Vermont and Quebec. Later surveys found similar lesions in nearby lakes in Maine and New Hampshire. Specifically, researchers estimate that 23% to 37% of the lake’s catfish carry the tumors.

How Does This Melanoma Spread Between Catfish?

Cancer cells break free from an infected fish and enter the surrounding water. From there, the cells apparently infect a new host directly. Julie Dragon, the study’s lead author, described the tumor as acting as its own infectious agent. Researchers confirmed this through genetics; tumors from different fish shared far more genetic material with each other than with their own hosts. In a typical cancer, that pattern simply does not happen.

Is Transmissible Melanoma in Catfish the First Case of Its Kind in Animals?

No, and this is where the story gets genuinely strange. Scientists have only confirmed transmissible cancer four times in the history of biology. Canine Transmissible Venereal Tumor spreads between dogs during mating and traces back 6,000 to 11,000 years to a single dog. Devil Facial Tumor Disease spreads between Tasmanian devils through biting and has emerged twice independently. Various bivalves, including clams, mussels, and cockles, pass leukemia-like cancers through seawater. Therefore, the catfish case joins an extremely small and unusual club.

Does Transmissible Melanoma in Catfish Pose Any Risk to Humans?

No, and the researchers were clear on this point. The American Cancer Society states that catching cancer from another person is essentially impossible. Cancer cannot spread through touch, shared food, or shared air. However, the case does raise interesting questions about how cancer cells generally evade immune systems. Scientists hope studying these catfish could reveal how tumor cells travel through a bloodstream in any species, including humans.

What Caused This Melanoma to Emerge in Catfish?

The honest answer is that nobody fully knows yet. Researchers initially suspected pollution from Hurricane Irene’s 2011 flooding damaged the lake’s water quality. However, water quality testing has not turned up anything abnormal so far. Fish of every age show the tumors, so a simple pollution timeline does not fully explain it either. As a result, the exact trigger remains an open scientific question.

My Experience: What This Discovery Means for Catfish Keepers

I keep several catfish species in my own tanks, specifically Panda Corys, Common Plecos, short-fin and long-fin bristlenoses. It is worth being precise here, since accuracy matters more than alarm. Bristlenose plecos belong to the Loricariidae family, while the affected Lake Memphremagog fish are Ictaluridae. Both fall under the order Siluriformes, but they are not close relatives. Furthermore, this transmissible melanoma has only been documented in one specific wild population so far. Indeed, there is currently no evidence linking it to aquarium-kept catfish species like plecos or corydoras. That said, this story is a good reminder to inspect your fish regularly for unusual skin changes. Any new, spreading, or unusual lesion on a catfish always deserves a closer look, regardless of species.