Angelfish difformity?

Hi, I have 3 angelfish in quarantine right now. Their bodies (fins excluded) are about the size of a nickel maybe a bit bigger. One of them seems to be missing a part of the base of its dorsal fin. There are tiny fin rays? where the base of the dorsal fin should be growing which I can only see when he fully extends his fins. But they are VERY small. I was wondering if anyone else has had angelfish like this and if it will eventually grow in. The other two in the tank have what appear to be normal dorsal fins.

I have a picture which isn't probably very good, but hopefully it will give you an idea of what I'm talking about.

I was worried that this might pose any future problems with the fish. One of the things I noticed is that when I first got them is they were all the same size, now the others have grown a few mm and he hasn't changed much in size. He eats and swims around actively, but he remains smaller than the rest. This was another cause for concern for me.

Thanks for your advice