Infection in gills

My angelfish has been acting some what lazy and today I was finally able to see why. It apparently has a infection of some sort in it's gills on one side. It has always had a small section of gill plate missing since I got it and have had it for a couple of years now. But today I see a white pin head sized object in that missing gill plate spot but attached to its gills. It moves with its gills as it breathes. I am sooo unsure of what this is or how to treat it. I have never came across this before. Has anyone else seen this before?? It's a beautiful long finned koi angel and I am wanting to try and use it for breeding as well so I want to try all ways to save it. It is still eating just fine and acts just as hungry as normal. It's just lazy and not swimming as much or holding it's fins as perky as normal but they aren't clamped either. Any advice would be great!