Scientists Discover Fourth Transmissible Cancer in Brown Bullhead Catfish

Researchers have identified a transmissible melanoma in brown bullhead catfish, marking the fourth known instance of a contagious cancer in the animal kingdom. According to reporting from Forbes and Nature, this discovery identifies a novel cancer that spreads between individual fish, rather than originating from a single animal’s own mutated cells.

The findings center on populations of brown bullhead catfish found in Lake Memphremagog, a body of water spanning the border between Vermont in the United States and Quebec in Canada. As reported by The New York Times and Yahoo, the cancer manifests as skin tumors that can be passed from one fish to another through direct contact.

Mechanism of Brown Bullhead Melanoma Transmission

Unlike typical cancers, which are caused by mutations within an organism’s own DNA, transmissible cancers involve the migration of live cancer cells from one host to another. In the case of the brown bullhead catfish, these cells act similarly to parasites, grafting themselves onto a new host and continuing to grow. According to Nature, this specific melanoma represents a distinct biological event where the cancer cells bypass the recipient’s immune system to establish a new tumor.

This discovery expands the known list of contagious cancers. Prior to this identification, scientists had documented only three other examples of transmissible cancers in wildlife: Devil facial tumor in Tasmanian devils, canine transmissible venereal tumor in dogs, and a similar contagious cancer in clams. The identification of the catfish melanoma provides a new data point for wildlife disease ecology and the study of how cancer cells can evolve to survive outside their original host.

Impact on Lake Memphremagog Wildlife

The spread of the disease has been observed within the specific ecosystem of Lake Memphremagog. Reporting from The New York Times indicates that the cancer is actively spreading through the catfish population in the lake.

Risk Assessment for Humans

The discovery of a contagious cancer in fish has prompted questions regarding potential risks to humans. According to Health and Me, there is no evidence to suggest that this specific form of transmissible melanoma can jump from fish to humans. Contagious cancers are typically highly species-specific, meaning the cancer cells require a compatible biological environment and a lack of immune rejection to survive in a new host.

The biological barriers between fish and mammals are significant, making the likelihood of cross-species transmission of this particular melanoma extremely low. Scientists view the discovery primarily as a breakthrough in understanding the evolution of cancer and the ecology of contagious diseases in aquatic environments rather than a public health threat.

Scientific Significance of the Discovery

The identification of the fourth transmissible cancer provides researchers with a new model to study how cancer cells can evade the immune system.

This discovery is particularly notable because it occurs in a different class of animals than the previously known examples. While the Tasmanian devil and dog cases involve mammals, and the clam case involves mollusks, the catfish discovery adds a ray-finned fish to the list, suggesting that the ability for cancer to become transmissible may be a more widespread evolutionary possibility than previously thought.