A collaborative study between Newcastle University and the Australian Institute of Marine Science published in the academic journal PLoS ONE - reveals the incidence of melanoma in the coral trout, a species found on the Great Barrier Reef and directly beneath the world’s largest hole in the ozone layer.

Widespread
“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,” explains Dr Sweet.

“Studying disease in wild fish populations is very time-consuming and costly so it’s hard to say how long the disease has been around. However, what we do know is that it is now widespread in the coral trout population effecting three different species of this type of fish and we would not be surprised to find it in other species as well.”

The study, which was funded by the Natural Environment Research Council (NERC), UK, and the Australian Research Council, involved experts from Newcastle University, the Australian Institute of Marine Science and James Cook University, Australia, and looked at Plectropomus leopardus, otherwise known as the common coral trout.

Basically healthy
Of the 136 fish sampled, 20 (15%) showed dark lesions on the skin – the lesions covered as little as 5% of the skin ranging to full coverage and an almost entirely black appearance. Dr Sweet said the numbers were significant.

“The individuals we looked at had extensive – but only surface – melanomas,” he explained. “This means the cancer had not spread any deeper than the skin so apart from the surface lesions 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. This suggests the actual percentage affected by the cancer is likely to be higher than observed in this study.”

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.

Crucial finding
In the lab, hybridised fish were found to be more susceptible to UV radiation due to exposure of the so-called ‘Xmrk’ gene. In the case of coral trout cross-breeding – or hybridisation – may also be occurring and play a role in the coral trout’s susceptibility to the disease. Dr Michelle Heupel from the Australian Institute of Marine Science stated: “This is a crucial finding in an iconic and high value reef species.
“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.”

Source information: “Evidence of melanoma in wild marine fish populations.” M J Sweet, N Kirkham, M Bendall, L Currey, J C Bythell, M Heupel. PLOS ONE. August 2012.
http://dx.plos.org/10.1371/journal.pone.0041989

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