Wantanabei angel with gill issue

[cabin]

I'm concerned about my Wantanabei angelfish. If has a dark line along the edge of the operculum that was not there originally. I saw a similar dark line once before, on my jawfish a year or so ago, and it subsequently died. Does this line mean something not good going on in the gills? I have had this fish only about a month. The dark line appeared two days ago. The fish is eating well.

I took two pictures, neither of which is great. (Actually I took dozens, but most were out of focus as the fish is very active):
http://reefcentral.com/gallery/data/500/57927wantanabei2Sm.jpg

Another one:
http://reefcentral.com/gallery/data/500/57927Wantanabei1Sm.jpg