Skin cancer found in fish

Skin cancer has been identified for the first time in wild coral trout populations in the Great Barrier Reef – directly beneath the largest hole in the ozone layer. Researchers from Newcastle University and the Australian Institute of Marine Science studied 136 fish in two offshore sites – Heron Island and One Tree Island – in the Great Barrier Reef Marine Park.

Of the fish sampled, 15% showed dark legions on the skin, which covered as little as 5% of the skin ranging to full coverage and an almost black appearance of the usually coral-coloured fish.

“The individuals we looked at had extensive – but only surface – melanomas. This means the cancer had not spread any deeper than the skin so apart from the surface lesions the fish were basically healthy,” said Dr Michael Sweet from Newcastle University.

“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 has only been observed in fish under laboratory conditions where it has been used as a model to study human skin cancer progression. Here, hybridised fish were found to be more susceptible to UV radiation due to exposure of the XMRK gene – coral trout cross-breeding may also be occurring and be a factor in the fish’s susceptibility to the disease.

“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,” said Sweet.

The next step in the study is to look at a much larger sample to determine the extent of disease presence and causation within the population. Anecdotal evidence suggests minimal occurrence in other regions of the Great Barrier Reef and in other coral trout species, although further research will be needed to confirm this.

• Evidence of melanoma in wild marine fish populations