Clown fish injury?
 

http://www.canreef.com/photopost/dat...SC00341mod.jpg

I just noticed today that the top part of my clown's dorsal fin is missing. I wish I had a better camera, but it looks as though only the flesh/membrane is missing and there's about 1mm of the first to spines showing.

Anyone have any ideas? Could this be an injury or an illness?

Thanks for looking

Myles