Mysterious Black Skin Cancer Spreading Among Fish Under Australia’s Ozone Hole Might Already Be In U.S.

By Mo Mozuch on August 4, 2012 12:28 AM EDT

photo:Michelle Heupel, Australian Institute of Marine Science
photo:Michelle Heupel, Australian Institute of Marine Science

Fried fish is on the menu for wild fish living in Australia's Great Barrier Reef. The Great Barrier Reef lies beneath the largest hole in the Earth's ozone layer, and the increased UV radiation is believed to be the prime culprit for an outbreak of skin cancer in coral trout species.

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In 2010, researchers at the Australian Institute of Marine Science in Townsville started noticing black, scaly patches on fish being eaten by sharks in the reef.  Initially, researches assumed the patches were caused by a microscopic pathogen such as fungus or bacteria.

"We can check for microbial pathogens quite easily. So we designed an experiment, screened for them, and couldn't find anything," Michael Sweet, a coral disease expert who was part of the research team, said. "So we had to look deeper."

Researchers began examining the tissue samples using microscopes, and soon discovered tumor-like formations. When they compared the samples with samples taken from fish given melanoma in a laboratory setting they noticed the cells in the wild fish were nearly identical.  The research found of the 136 coral trout sampled, 15 percent showed dark lesions on the skin. After two years of research and documentation, the scientists finally published their findings in PloS One on Wednesday. 

In addition to ozone-hole radiation, researchers attribute cross-breeding between different species of coral trout as a potential cause.  They theorize that cross-breeding is producing offspring more prone to cancer due to the loss or mutation of certain genes, but can't be certain until genetic testing has been done to the affected fish. Pollution has been ruled out as a culprit because environmental protections on the Great Barrier Reef have left it virtually pristine.

Sweet told the Huffington Post that "the findings are strongly linked to UV and it's too much of a coincidence for it not to be linked to the hole in the ozone layer." Australia, which also sits beneath the ozone hole, has the highest rate of skin cancer in the world, with 2 out of every 3 adults expected to be diagnosed with it before they reach 70 years-old. Sweet's team contends that they have discovered the first instance of malignant skin cancer in wild fish, a claim being disputed by American scientist Vicki Blazer.

Blazer, a pathologist at the U.S. Geological Survey's National Fish Health Research Laboratory in Kearneysville told Sciencenews.org that Sweet and his team should "go back to the library and look a bit more." Blazer served as lead author of a 38-page report documenting a range of liver and skin legions in brown bullhead fish. The report contains several sections on melanoma, and Blazer contends that there have been at least 10 academic papers published in the last several decades confirming the existence of melanoma in wild fish.  Other experts are questioning if the black splotches are melanoma, which is malignant, or if the discoloration is actually a benign phenomenon.

Wolfgang Vogelbein of the Virginia Institute of Marine Science in Gloucester Point told Sciencenews.org that the images accompanying the PLoS One report lack telltale signs of malignancy, such as misshapen cells or local invasiveness.  "The characteristic cellular features of malignancy, well, they're just not there," he said.

Michael Stoskopf, a toxicologist and aquatic clinician at North Carolina State University's College of Veterinary Medicine in Raleigh, agrees with Vogelbein. To him, the blotches appear to be "a mole or liver spot that comes with aging - not a malignant cancer that's going to spread into other organs." Blazer agrees that the cells do not appear to be malignant skin cancer, but she admits that "there's definitely something wrong here." And not just in Australia's Great Barrier Reef, Blazer has seen "very similar" black splotches appearing on fish in the U.S.

Smallmouth bass in Pennsylvania's Susquehanna River began developing the blotches in the last year, according to the Pittsburgh-Post Gazette. Officials from the Pennsylvania Fish and Boat Commission claimed to have found up to 40 percent of adult smallmouth bass afflicted with the hyperpigmentation in a survey conducted last fall. Theories range from increased UV penetration into shallower waters to hormone-mimicking pollutants in the water supply. One thing is certain, however, the need to know more.

"We just don't know," Blazer said. "It's something we need to investigate more."

© 2012 iScience Times All rights reserved. Do not reproduce without permission.

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