Scientists discover 1st known likely transmissible cancer in wild catfish - Yahoo

What the report says

ABC News reports that researchers have identified what appears to be the first known transmissible cancer in wild fish, involving brown bullhead catfish from Lake Memphremagog, a freshwater lake crossing the Vermont–Quebec border. The finding is based on a new study published in Nature and stems from a mystery first noticed in 2013, when anglers and biologists began finding catfish with raised black spots. According to the study cited by ABC, 23% to 37% of sampled fish had confirmed melanoma lesions.

Scientists initially considered whether environmental contamination might explain the unusually high cancer rate, especially after major flooding from Tropical Storm Irene in 2011. But researchers found no infectious agent that explained the tumors. Using whole-genome sequencing, they compared cancerous tissue with healthy catfish tissue and found that tumors from multiple fish were highly similar to each other while differing from the fish carrying them. That pattern suggests the tumors descended from one cancer cell lineage that spread among fish, rather than arising separately in each animal.

ABC notes that researchers have not yet determined exactly how transmission occurs. Brown bullheads gather closely during spawning, which may provide opportunities for cancer cells to move between hosts, but the route has not been proven. The report also emphasizes that there is no known risk to people from the catfish cancer, despite Lake Memphremagog serving as a drinking water source for more than 175,000 people.

Previously documented naturally transmissible cancers have been found in dogs, Tasmanian devils and bivalve mollusks. Scientists say the catfish discovery could help clarify how some cancer cells evade immune defenses, survive outside their original host and continue growing.