August 2, 2012

Fish With Skin Cancer?

Fish With Skin Cancer?

By: Erika Dunayer, Ivanhoe Health Correspondent

(Ivanhoe Newswire) -- Melanoma is the most dangerous type of skin cancer and is the leading cause of death from skin disease. Over 9,000 people die from Melanoma every year in the United States. Researchers are now starting to see evidence of the disease in fish!

A collaborative study between Newcastle University, UK, and the Australian Institute of Marine Science 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, says the appearance of the melanoma is almost identical to that found in humans.

"We initially thought it was a fungal disease," Dr. Michael Sweet, a microbiologist studying the epidemiology of coral reefs, told Ivanhoe.

"We managed to find out that it was actually skin cancer through direct comparisons to models for human melanoma," said Dr. Sweet.

The study, which involved experts from Newcastle University, the Australian Institute of Marine Science and James Cook University, Australia, looked at Plectropomus leopardus, otherwise known as the common coral trout.

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. Of the 136 fish sampled, 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.

"The high prevalence is pretty surprising. We found 15% of a population, which is very unusual because we are putting this down to UV being the causal factor for the melanoma“¦It is pretty devastating," Dr. Sweet said.

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, hybridized 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 hybridization — may also be occurring and play a role in the coral trout's susceptibility to the disease.

"You might expect quite a low percentage of the population to contract something like this because it is thought to be down to a genetic pre-disposition. When you get two different species with the same gene of 'coral trout' but two different species, which is called hybridization, most of the time is quite good because it causes evolution. Every now and again you get quite bad defects. You would expect that maybe in 1 or 2 percent of a population, but 15% is really quite surprising," added Dr. Sweet.

Is this highly commercial fish safe to eat?

"We can't say that it is 100% safe to eat, it's likely to be alright but we really need to look further into that," Dr. Sweet concluded.

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.

Source: Interview with Dr. Michael Sweet, Microbiologist, August 1, 2012