what is this on my fish?

[penske38]

Can anyone tell me what is the on my fish. I've had the fish for well over two years and it has been there for the majority of that time. In the picture, it is the white-looking spot above the fish's eye. This is a chocolate tang.
http://www.blackberry.com/VirtualPreload/?url=http://m.yp.com/app&language=en