Skin cancer found in Great Barrier Reef fish

A healthy coral trout – the diseased fish are identified by dark lesions. Richard Ling

Scientists have identified skin cancer in the Great Barrier Reef’s wild fish populations which is almost identical to melanomas found in humans.

The team of researchers from the Australian Institute of Marine Science and Newcastle University in the United Kingdom caught the diseased coral trout, or Plectropomus leopardus, in two locations in the southern Great Barrier Reef Marine Park – Heron Island and One Tree Island.

Of the 136 fish sampled, 15% showed dark lesions on the skin, which ranged from 5% coverage to an almost entirely black appearance.

UV-induced melanoma in fish has until now only been seen under laboratory conditions and has been used as a model to study the progress of human skin cancer due to the similarities in the disease.

The findings are published today in the journal PLoS ONE.

“Beyond health implications for individual fish, this syndrome may have implications for the population as a whole and the commercial and recreational fisheries that exploit this species,” the study said.

While the sample of infected fish had extensive surface melanomas, the cancer had not spread deeper than the skin, meaning the fish were basically healthy.

“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,” said lead author Dr Michael Sweet from the University of Newcastle.

“This suggests the actual percentage affected by the cancer is likely to be higher than observed in this study.”

Study co-author Dr Michelle Heupel from the Australian Institute of Marine Science said there was likely to be a genetic component to the high rates of melanoma in the coral trout. Another contributing factor was that the fish lived close to their temperature threshold, which could compromise their immune system.

“It may just be that they’re living close to the edge there and this genetic composition makes them a little more susceptible,” she said. “And that’s combined with UV exposure in the region. I really think it’s the combination of all those factors working together rather than one thing independently.”

Local commercial and recreational fishers have indicated they have seen fish with black spots for as long as they can remember, Dr Heupel said. “I don’t think the disease is new, it’s just the first time anyone has stopped to look at it.”

Professor Carlos Duarte, Director of the University of Western Australia’s Oceans Institute, said the human health problems caused by UV radiation were well known – with rates of skin cancer nearly four times that of Canada, the United States and United Kingdom – but the effects of UV radiation on marine life had not been systematically assessed.

“It is very likely that the general decline of marine life in the past three decades reflect the compound effects of multiple stresses, including that to UVB radiation, and not warming alone,” he said.

“Understanding the role of elevated UVB radiation as an additional driver of the decline of marine life is of fundamental importance to predict and catalyse, through effective managerial actions, their recovery.”