Lesions presented on sampled coral trout, Plectropomus leopard. (Photo: ncl.ac.uk/ Sweet et al)

Melanoma found in wild marine fish

UNITED KINGDOM
Thursday, August 02, 2012, 23:50 (GMT + 9)

A new study has identified widespread skin cancer in wild marine fish populations for the first time. The study describes the incidence of melanoma in 15 per cent of coral trout (Plectropomus leopardus) on the Great Barrier Reef and directly underneath the largest hole in the planet’s ozone layer.

The results of the collaborative study between Newcastle University, UK, and the Australian Institute of Marine Science were published in the academic journal PLoS ONE.

Led by Newcastle University's Dr Michael Sweet, the team claims the appearance of the melanoma is nearly identical to that found in humans.

"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," explained Sweet.

The scientists do not know for how long these fish have been suffering from cancer.

"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," he added.

Diseased fish were collected in two locations in the southern Great Barrier Reef Marine Park. Anecdotal evidence suggests minimal occurrence in other regions of the GBR and in other coral trout species.

Of the 136 fish sampled, 20 (15 per cent) showed dark lesions on the skin which covered 5 to 100 per cent of the skin and had an almost entirely black appearance. Dr Sweet called these numbers significant.

"The individuals we looked at had extensive – but only surface – melanomas," he said. "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," Sweet continued.

In contrast, three outside experts read the study and each concluded independently that the new lesions may not actually be cancers, Science News reports.

But even if they were, these skin cancers are not unique in wild marine fish, they said: Vicki Blazer, a pathologist at the US Geological Survey’s (USGS) National Fish Health Research Laboratory in Kearneysville, West Virginia, explained that skin cancers affecting fish in the Great Lakes and Chesapeake Bay have been reported “for decades.”
 
It is possible that trout cross-breeding – or hybridisation – may be taking place and playing a role in the coral trout's susceptibility to cancer, the team noted.

The next step in the study is to analyse a much larger sample and determine the extent of disease presence and causation within the stocks.

Moreover, research on the potential links of this melanoma to increases in UV radiation from stratospheric ozone depletion needs to be completed, according to the scientists.

By Natalia Real
editorial@fis.com
www.fis.com

Print