Skin Cancer Seen In Wild Fish For First Time; Ozone Hole Suspected

Australians who live beneath the largest hole in the planet's ozone layer are careful to take measures to avoid skin cancer. Now it seems Australia's fish are in need of some protection as well -- a new study has identified a significant plague of skin cancer cases among coral trout on the Great Barrier Reef.

This is the first time skin cancer has been diagnosed in a wild fish population in the sea, according to the authors of a new paper in the journal PLoS ONE.

The melanoma the scientists found on the fish is nearly the same kind that affects humans, according to study author Michael Sweet of Newcastle University.

"Further work needs to be carried out to establish the exact cause of the cancer, but having eliminated other likely factors such as microbial pathogens and marine pollution, UV radiation appears to be the likely cause," Sweet said in a statement Wednesday.

Sweet and his colleagues caught 136 fish, 20 of which had dark lesions on their skin. Some fish were only partially covered with lesions, but in some cases were almost entirely covered, which made them appear blackened.

The fish the researchers found only had surface melanomas, meaning the cancer had not encroached any further than the skin.

"Once the cancer spreads further you would expect the fish to become quite sick, becoming less active and possibly feeding less, hence less likely to be caught," Sweet said. "This suggests the actual percentage affected by the cancer is likely to be higher than observed in this study."

Until now, the only skin cancer seen in fish caused by UV radiation was in laboratory specimens used to model human disease.

Co-author Michelle Heupel from the Australian Institute of Marine Science said in a statement that the finding was crucial.

"Given climate change scenarios and continuing alteration of coral reef environments, understanding the cause of this disease is important to continued conservation and management of reefs and their inhabitants," she says.

Pet fish are also known to get tumors and cancer, usually visible as lumps underneath the skin. Usually these cancers are caused by viral infections or because of a genetic condition.

Sharks can also get cancer, despite some very stubborn myths that they can't. As writer Christie Wilcox explained at Scientific American, the tale of the cancer-resistant shark was popularized by a man named I. William Lane, who incidentally also owns a company that makes and sells pills made from shark cartilage.

Lane drew from studies showing that shark cartilage, like other forms of cartilage, can prevent blood vessels from linking up with tumors to supply them with blood, and a single study of nurse sharks that did not develop tumors after being exposed to known carcinogens.

Aside from the fact that the shark supplements don't work and contribute to the decimation of shark populations, it turns out sharks actually do get cancer. In a 2004 Cancer Research paper, scientists pointed to 42 cases of tumors in sharks and their relatives that have been documented throughout the last 150 years or more.

"Even if we hadn't found cancer in sharks, it's highly unlikely that they alone are cancer-free. It's far more likely, instead, that the perceived 'low rates of cancer' are due to the fact that there has yet to be even one study which looked at the rates of disease in sharks," Wilcox wrote.

SOURCE: Sweet et al. "Evidence of Melanoma in Wild Marine Fish Populations." PLoS ONE 7: e41989, 1 August 2012.