white circle on blue hippo tang

[dive1]

I have a blue hippo which I bought about a week ago. He has a white circle about the size of a dime on one side (1/8in white line forming a circle) about 1in from tail. If it was on a human I would say ring worm. What is this and what should I do about it? The inside of the circle seems to be starting to turn white also.

 

[beth]

Gee, never heard of that before. If you had said around the head or lateral line area, I would have though lateral line disease. Did the fish have this when you got him?
Can you get a pic up?

 

[dive1]

Not sure what it was but it is too late now. He passed durning the night. Everyone else looking ok.