I have a "captive breed" blue tang in qt going on 3 weeks. It is just and observation QT. Fish has a transparent spot just above its anal fin. I can see light shine through the fish from the other side. It looks like the fish has lost pigment. On one side it's about half a pencil eraser. On other it's like a 1/8 of a pencil eraser. Fish swims to fast to get a picture. But the fish eats everything and is very social. No other signs of illness.