Scientists Discover the First-Ever Contagious Cancer in Fish - Gizmodo

What the report says

Gizmodo reported that researchers have identified what they say is the first documented contagious cancer in fish, after studying melanoma tumors in brown bullhead catfish from Lake Memphremagog, a freshwater lake spanning Vermont and Quebec. The findings, published Wednesday in Nature, center on black skin lesions that local biologists and fishers had increasingly noticed in the lake since 2012.

According to the report, scientists at the University of Vermont compared tumors from affected catfish with healthy tissue from the same fish and from unaffected catfish. Instead of finding ordinary cancer mutations tied to each individual animal, they found the tumors were genetically far more alike to one another than to their hosts. Whole-genome sequencing showed large numbers of shared genetic variants among the tumors, supporting the conclusion that the cancer lineage is spreading between fish.

The discovery is significant because transmissible cancers are rare in animals. Gizmodo noted that such cancers had previously been identified in dogs, Tasmanian devils and several bivalve mollusks, but not in fish or any freshwater animal. The researchers also examined other possible explanations, including pollution from a nearby landfill, but the report says affected fish have been found across the lake and in other New England waters, including areas without obvious major pollutant sources.

Important questions remain, including how the cancer moves between catfish, how much harm it may cause to populations and how it evades immune defenses. The researchers suggested spawning behavior, lake-bottom exposure and environmental factors such as arsenic may warrant further study, while emphasizing that the cancer is not considered a threat to humans.