I'm posting this for a friend who just got a blue angel.
He's in a 72 gal tank currently.
He was added ~2 weeks ago and is eating well.
He just noticed these spots on the tail yesterday.
I believe these look like ich, but I would like to get a second opinion.
Disclaimer: I make absolutely no claims to know anything at all about aquatic disease, and definitely not saltwater diseases. All opinions offered are based on gut instinct/limited general knowledge and are subject to change. I would suggest getting second opinions before acting based on my advice. I am not responsible in any way for loss resulting from making decisions based on my advice.
Ok, now that that's out of the way, if I saw it in my tank I say it was natural, particularly since nothing has changed in a week. If he's acting fine, I wouldn't worry.
I would say Ich. The 72 gal is way too small for that angel in the long term - it is after all a large angel that will get well over a foot long. He either already had Ich and broke out from the stress of putting in small tank, or the tank itself is already infected with Ich. More information needed to rule out Ich though: Was the tank Ich free (not Ich outbreak free, but Ich free)? Any chance the angel could have brought in Ich and infested the tank?
No mention about QT was made, so there was no QT? Then it is likely that both the tank was already infected and the fish brought in Ich as well.
Hopefully I am wrong and it is something different than Ich, as that will be a pain to get out of the tank. My 180 currently has an Ich problem - only solution for me right now is trying to keep the fish alive until I can setup a large enough hospital tank big enough to keep the fish in for a couple months so I can get rid of the Ich in DT.