New Transmissible Cancer Identified in North American Catfish

WHO:

Forbes - Peter Emerson, a fish biologist with the Vermont Fish and Wildlife Department.

Forbes - Julie Dragon, associate professor of microbiology and molecular genetics at the University of Vermont.

WHAT:

Wired - Scientists identified the first known transmissible cancer among freshwater fish.

Forbes - The melanoma found in bullhead catfish is contagious, spreading from one fish to another as living cancer cells.

Forbes - The melanoma is the fourth type of transmissible cancer known to science, the first in fish and the first in fresh water.

Forbes - In 2012, an angler discovered a brown bullhead with unusual growths in Lake Memphremagog.

Forbes - By 2015, black growths were observed on 25% to 40% of the lake’s bullhead population.

WHERE:

Wired - The transmissible cancer was identified in Lake Memphremagog, which spans the US and Canada.

Forbes - The disease has been found in New Brunswick, Nova Scotia, Maine, New Hampshire, Massachusetts, Pennsylvania, Wisconsin, and New York.

WHEN:

Forbes - The angler brought the affected fish to Peter Emerson in 2012.

Forbes - The researchers reported their findings in Nature this week.

Forbes - The team re-surveyed the lake in 2017.

WHY:

Forbes - Researchers initially sought common causes for the cancer, such as chemical carcinogens or infections, but found no evidence of these.

HOW:

Forbes - The cancer is described as a "clonal cancer," meaning it is not driven by a bacteria or virus but is the infectious agent itself moving from fish to fish.

Forbes - The researchers conducted genomic analysis to understand the relationship between the tumors and the host fish.

(UPDATED July 25, 2026 09:27 UTC)

Scientists have identified the first known transmissible cancer among freshwater fish, specifically a contagious melanoma found in bullhead catfish, which spreads through living cancer cells. This groundbreaking discovery, reported in Nature this week, marks the fourth type of transmissible cancer known to science and the first identified in fish and freshwater environments. The disease was first noted in 2012 when an angler brought an affected fish to Peter Emerson, a fish biologist with the Vermont Fish and Wildlife Department, and has since been observed in various locations including New Brunswick, Maine, and New York.