A collaborative study between Newcastle
University and the Australian Institute of Marine Science published August 2 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. This is the first time skin cancer
has been diagnosed in wild fish populations and the team, led by Newcastle
University's Dr Michael Sweet, say the appearance of the melanoma is almost
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," 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.
The coral trout is an iconic and highly valued
species that occurs throughout the western Pacific and in Australia supports a
high-value fishery on the Great Barrier Reef. Diseased fish were caught in two
locations in the southern Great Barrier Reef Marine Park -- Heron Island and
One Tree Island -- but its occurrence throughout the rest of its range is
currently unknown. Anecdotal evidence suggests minimal occurrence in other
regions of the GBR and in other coral trout species, but further research is required
to confirm this.
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. 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."
The next step in the study is to look at a much
larger sample and determine the extent of disease presence and causation within
the populations.
More at: 1. Michael Sweet, Nigel Kirkham, Mark Bendall,
Leanne Currey, John Bythell, Michelle Heupel. Evidence of Melanoma in
Wild Marine Fish Populations. PLoS ONE, 2012; 7 (8): e41989
DOI: 10.1371/journal.pone.0041989
No comments:
Post a Comment