Evidence of Melanoma in Wild Marine Fish Populations

Abstract

The increase in reports of novel diseases in a wide range of ecosystems, both terrestrial and marine, has been linked to many factors including exposure to novel pathogens and changes in the global climate. Prevalence of skin cancer in particular has been found to be increasing in humans, but has not been reported in wild fish before. Here we report extensive melanosis and melanoma (skin cancer) in wild populations of an iconic, commercially-important marine fish, the coral trout Plectropomus leopardus. The syndrome reported here has strong similarities to previous studies associated with UV induced melanomas in the well-established laboratory fish model Xiphophorus. Relatively high prevalence rates of this syndrome (15%) were recorded at two offshore sites in the Great Barrier Reef Marine Park (GBRMP). In the absence of microbial pathogens and given the strong similarities to the UV-induced melanomas, we conclude that the likely cause was environmental exposure to UV radiation. Further studies are needed to establish the large scale distribution of the syndrome and confirm that the lesions reported here are the same as the melanoma in Xiphophorus, by assessing mutation of the EGFR gene, Xmrk. Furthermore, research on the potential links of this syndrome to increases in UV radiation from stratospheric ozone depletion needs to be completed.

UV-induced DNA damage in coral reef fish: damage levels and protection mechanisms

“…Recently it has been suggested by Sweet et al (2012) that UVR exposure and UV-induced DNA damage could be the likely cause of melanoma in coral trout (Plectropomus leopardus) from the southern Great Barrier Reef. In the samples collected near LIRS, no evidence was found for higher than normal levels of DNA damage in adults of this species, and the two larval specimens had the lowest levels of DNA damage of all the species examined.…”

“…Also, no external signs of melanoma or changes in skin colouration or ulcers were observed in any of the individuals included in this study. The cause of the high rate of melanomas in wild population of reef fish therefore remains unknown for now, but could well be explained by considering the potential for genetic mutations (Sweet et al 2012) and their influence on the rate of occurrence of melanomas in reef fish.…”

“…Leech (2003)) is that reef fish should be well protected due to their evolutional history in the tropics. However, recently, the occurrence of melanoma in coral trout (Sweet et al 2012), an ecological and commercial key species (Harrison et al 2012), has been linked to UVR after a range of other pathogens were ruled out. It therefore appears that fish are vulnerable to UVR despite the various protection mechanisms.…”

“…The accumulation of net DNA damage over time however (Mitchell et al 2009), shows that sunscreens, DNA repair and behavioural avoidance are not able to provide complete protection from UVR. Considering the high amount of UVR that reaches coral reefs (Dunne & Brown 1996) compared to temperate regions, it is surprising to see that UV-induced DNA damage and its impacts on coral reef fish has been addressed only marginally in a small number of studies (Zamzow 2004, Sweet et al 2012). …”

“…ROS are mostly generated by UVA, while the absorption of UVB predominantly leads to the formation of dimers in the DNA (Friedberg 2003). These cyclobutane pyrimidine dimers (CPDs) lead to mutations and cell death if unrepaired (Ikehata & Ono 2011) and have been linked to reduced growth (Lesser et al 2001), formation of melanomas (Sweet et al 2012) and increased mortality (Dong et al 2007, Tucker et al 2010, Fukunishi et al 2013b) in fish from temperate and tropical waters.…”