Injured Percula Clown

I recently purchased 2 percula clowns, not sure if they are black perc's or not as they have only a small amount of black on them but are not bright orange.

Anyways i noticed shortly after i had introduced them to my tank the th larger of the 2 had what appeared to be a rather large gash on the side of its head. Naturally i was cursing at myself for not noticing this at the LFS and waited for it to die and belly up.

Only it didnt. The little fella just kept swimming around happily. Upon closer inspection i saw it was not a cut but rather part of the fish's gill flap thingy (gill cage?) was missing and what i took to be bright red blood was actually its gills!
As far as i can see theres no exposed flesh theres just a bit of him missing.

Could it be maybe an old wound that has since healed over? Is this going to be a major problem for him in the future?
Thanks in advance for any input here

 

Heres a pic. You cant really see much detail but in reall life i can actually see his individual 'gill bits' (ok heres where my fish jargon runs out )

 

Treat him with antibiotics....i cant tell for sure but it looks to be very close if not on the gill......very bad news if a bad infection sets in.....i would promptly treat him with somthin that ends with cylin........any good antibiotic.