Australian fish have high incidence of skin cancer too

Fish with cancer discovered in Australia. Image: Newcastle University/Michael Sweet

Widespread skin cancer has been identified in coral trout species in the Great Barrier Reef.

Living in Australia, underneath the world’s largest hole in the ozone layer, we are all taught the rule “slip, slop, slap” from a young age. Along with New Zealand, Australia has the highest incidence rate of melanoma in the world.

There is much research being conducted into human skin cancer, but studying the disease in wild animal populations has proven to be much more difficult and costly in the past.

A collaborative new study between experts from Newcastle University, UK, and the Australian Institute of Marine Science has revealed for the first time that there is a high prevalence of melanoma in at least three different species of the iconic coral trout (Plectropomus leopardus) in two locations (Heron Island and One Tree Island) on the southern Great Barrier Reef Marine Park. The results of this study have been published in the journal, PLoS One.

“The strong links between our samples and those in laboratory UV induced melanomas [in fish], suggests UV-B to be the most likely cause of cancer in [wild populations] of fish,” says lead scientist Michael Sweet from Newcastle University. “This coupled with the highest prevalence of cases reported being directly under the ozone hole in the southern hemisphere strengthens our hypothesis.” Although, Sweet explains, further work to confirm this is ongoing.

During the field research the scientists sampled 136 fish and found that 20 (15%) of them were covered in lesions on the surface of their skin indicative of melanoma.  These lesions ranged from just a few small cuts, to full skin coverage, which gave the usually vibrant coloured fish an entirely black appearance. In all the diseased fish, the cancer was restricted to the dermis and in its early stages.

The researchers tested whether other possible environmental factors could be causing the prevalent skin disease, such as microbial pathogens or marine pollution. But analysis showed the amount of microbes to be equal in the diseased and non-diseased fish. Therefore, according to the researchers, UV radiation appears to be the most likely culprit.

UNSW researcher Bart Adriaenssens, who was not involved with the study, explains that the research is very interesting and can count as a warning signal that increased UV may not only affects humans but also wild animal populations. Apart from this it also underscores the need for further research to better understand the occurrence of melanoma in nature.

“Even if ozone layer thinning is a very likely candidate, future research is needed to fully rule out alternative causes for the melanoma: do we notice it only now because research focuses more on skin cancer these days? If it is a recent syndrome, can it be caused by a recent shift in activity of coral trout that exposes them more to UV?, [for example]  coral trout may have shifted their activity towards UV-rich surface layers in response to changes in prey or predator abundance leading to similar increases in melanoma prevalence,” says Adriaenssens. “However, the study clearly confirms that melanoma exists in natural coral trout populations and these questions now become relevant.”

How far reaching and concerning the disease is also remains unclear and the researchers say there are many environmental and economic factors that need to be considered. “As it’s [coral trout] a commercially valuable fish there are potential economic implications of the disease to this trade and also human health issues need to be further investigated,” says Sweet.

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