a) a fish with a lesion covering 10% of its body surface; b) another with almost complete coverage; c) healthy tissue under light microscope; d) the lesion. (source linked below)

A new study, published August 1,2012, said that the sun is giving fish skin cancer.

Researchers caught and studied coral trout, off the East Coast of Australia (Heron Island and One Tree Island) and found that 15% of them had skin cancer. The lesions covered 10% to almost 100% of the fish’s body surface.

Fish disease due to infection is common (viral, bacterial, fungal), especially when they are farmed, due to closed quarters. Skin cancer, however, is quite unheard of. Cancer in fish has been induced before in labs by exposing the fish to UV radiation, but you don’t often come across a fish in the coral reefs with skin cancer.

Wait, fish have skin??

It might sound a bit odd to someone who never really thought about it before, but fish do have skin, complete with epidermis and dermis, and melanin cells capable of turning cancerous just like humans. Histology of the diseased skin in the tested fish showed increased melanin cell density and depth, as well as a disorganization of the natural pattern of melanin.

What’s causing it?!

Researchers considered infection, but all tests of microbes came back normal. Added to that, the fish studied were caught in a marine protected area with no reports of pollution. So the researches could think of one possible culprit: the sun.

Heron Island

The appearance and histology of the lesions seen in the affected fish resembled lesions of skin cancer induced by UV radiation in lab fish. The tested coral trout were caught in Australia, an area particularity vulnerable, given its proximity to the Antarctic ozone hole. UV rays penetrate as deep as 60 meters under the water. In this study, the fish were all captured from depths of 20 meters only, in waters that are very clear, in an area with a high UV index, making them much more susceptible to UV radiation.

So what do we take from this study?

Aside from suspecting UV radiation, researchers also believe a genetic mutation – resulting from cross breeding between the fish in the reef – has lead to an offspring more susceptible to skin cancer. So was it just the sun, the genes, or both?

Until this debate is settled, the rising prevalence of skin cancer, first in humans and now fish, is certainly food for thought. It’s not like they can wear sunscreen! But in summary:

1. We only have this one earth, if we keep poking holes in the ozone, we’re uhh… in a bit of a pickle! More effort needs to be dedicated to being kinder to the environment.
2. Until that problem is fixed (and even after it is!): commit to sunscreen! The poor fish cannot use it, but we’re lucky enough that we can!

Thanks for reading!

Source

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0041989#pone-0041989-g001