Maybe it's time fish use sunblock. A new study has found the first skin cancers in wild fish, specifically in coral, bar-cheeked, and blue spotted trout swimming on Australia's Great Barrier Reef. The lesions and dark patches are a scalier version of what melanomas look like on humans, but it's unclear whether they make the animals unsafe to eat.
Scientists know how to give fish skin cancer in the lab. They breed a swordtail and a platyfish, both common pets, to create offspring that are more sensitive to UV light. The reason is genetic. Platyfish have a so-called tumor gene and a regulator to control it, whereas swordtails have neither. When the two mate, their offspring will sometimes inherit only the tumor gene without the regulator, leading to increased incidence of various cancers. These offspring crosses have been used to study skin cancer in humans. But researchers were unsure whether fish got the disease in the wild.
The first hint that they did came when a group of marine biologists at the Australian Institute of Marine Science in Townsville, who were studying sharks on the country's Great Barrier Reef, noticed that the coral, bar-cheeked, and blue spotted trout being eaten by the sharks had black patches on their skin. At first, the researchers thought the patches might be caused by a fungus. But when they sent tissue samples from the fish to colleagues at Newcastle University in the United Kingdom, the U.K. scientists found no evidence of microbial infection. What's more, the Australian group found no pollutants in the highly protected Great Barrier Reef that would have caused such discoloration. That left one main suspect: skin cancer.