Will healthy angelfish pick on injured angelfish?

In my limited experience with angels, I've noticed that they don't like change. What I mean is if you get a group of 7 and they get along for months, you can't add 1 more or it will be attacked. If 1 or 2 die, you can't replace them. Once the group has established itself, they will defend the upper levels against all newcomers. At least that's been my experience.

Sent from my DROIDX using MonsterAquariaNetwork App

I have seen similar with my angels as well. The pecking order has been disturbed.....and must be re-established. They may leave him alone after a bit, you will have to monitor the situation. I would wonder if the reason he got stuck was because he was trying to hide from the others. We don't always see the aggression.....

Angels are conspecific aggressive.. meaning they will attack their own species.

it sounds as if you have 2 pairs of angels (paired as in breeding pairs?) already in the tank. and they are attacking the ..odd fish out...

how big is this tank??

In many species a sick or injured fish will be attacked to drive them away. This is especially true of cichlids. It's not so much a territory issue as it is a fitness issue.

This type of behavior is not limited to fish. You will find it in many species including humans. What the others have said is also true. Once you remove the sick/injured fish from the "pool", the only way you can return it is to first rearrange decor to upset established territories, feed the original ones, and then reintroduce the new one at night. This works many times but not all times. Sometimes, no matter what you do you cannot introduce new or reintroduce a once injured/sick fish.

Good luck.