# Contagious Cancer Discovered in North American Catfish Transmissible melanoma in catfish surprises the scientific community. - **Source:** [Science Latest](https://brifing.si/source/ebc20f22-8d1a-4ae4-ba4c-efcd0853ba19) - **Published:** 2026-07-25 - **Topic:** [Business](https://brifing.si/c/business) - **Original article:** - **On Brifing:** https://brifing.si/s/3d88a462-a493-4383-97f8-07315fb1dec5 ## Nature's Surprising Reality Researchers detected transmissible melanoma in brown catfish, marking the first recorded case in fish and in freshwater ecosystems. This rare phenomenon, where cancer cells can pass from one fish to another, has caused significant ripples in the scientific world. ## Mysterious Lesions In 2012, an abnormal increase in catfish with black lesions was noted in Lake Memphremagog, spanning Vermont and Quebec. Studies revealed these were malignant melanomas, affecting 23-37% of examined fish—an unusually high rate for the species, raising immediate scientific curiosity. ## Cracking the Genetic Puzzle Genetic analysis yielded a startling revelation: tumor cells from different fish were more closely related to each other than to their hosts. This strongly suggested the cancer wasn't arising independently but was spreading contagiously among the catfish population. ## Transmission Mechanism Unknown How the cancer spreads remains unclear. Hypotheses include close contact during spawning, tumor cells surviving in water/sediment, or hormonal changes weakening immunity. Notably, younger fish show no signs of the disease, hinting at age or reproduction-linked factors. ## Arsenic Connection Elevated arsenic levels were found in tumor cells, with geographic overlap between cancer prevalence and natural arsenic-rich areas. However, researchers caution this correlation doesn't prove causation. Whether arsenic triggers or facilitates the cancer remains an open question. ## Implications for Human Cancer This discovery opens new research avenues. Understanding how cancer cells survive and spread beyond their original host could reveal mechanisms relevant to human cancers. Scientists highlight potential clinical insights into how cancers breach biological containment in patients. ## Sources covering this story - https://www.wired.com/story/contagious-cancer-found-in-north-american-catfish/ — --- _Summary written by Brifing from the original reporting. Copyright in the original article belongs to its publisher; read the full piece at the link above._