# First Known Transmissible Cancer Discovered in Fish Rare contagious melanoma identified in catfish from Quebec. - **Source:** [Slashdot](https://brifing.si/source/0f34d58e-1ccd-45a6-ab82-2de4065dc7ad) - **Published:** 2026-07-23 - **Topic:** [Business](https://brifing.si/c/business) - **Original article:** - **On Brifing:** https://brifing.si/s/e18dcc82-f4b5-481a-a732-cf1621f9895e ## A Rare Phenomenon Scientists have discovered that melanoma tumors can spread between individual catfish in Quebec and the northeastern U.S. This marks the first known case of transmissible cancer in fish. Such occurrences are extremely rare in nature. ## Appearance of Strange Spots In 2012, fishermen in Lake Memphremagog noticed black spots and lumps on catfish. Examinations revealed these to be melanoma skin cancer tumors. Now, about one-third of the catfish in the lake exhibit these growths. ## Effects of the Cancer The full impact of the tumors on the fish's health remains unclear. In some cases, the cancer has spread to organs like the brain or liver. However, many fish appear relatively healthy despite the tumors, with older fish even surviving with them. ## Suspected Environmental Factors Locals initially suspected carcinogens washed into the lake during a 2011 flood might be responsible. While tests have been inconclusive, higher concentrations of metals like arsenic were found in the skin of affected fish. ## Transmission Mechanism Researchers believe the tumors may spread during spawning when fish rub against each other and may be punctured by spines. This physical contact could allow cancer cells to transfer between individuals, though direct evidence is still lacking. ## Significance for Science This discovery holds major implications for understanding transmissible cancers in nature. Previously, only three other species (Tasmanian devils, dogs, and shellfish) were known to host such cancers. This first fish case could shed light on cancer's evolutionary pathways. ## Sources covering this story - https://science.slashdot.org/story/26/07/23/0610239/researchers-discover-first-known-transmissible-cancer-in-fish?utm_source=rss1.0mainlinkanon&utm_medium=feed — --- _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._