I tried getting a photo of him in the tank but it's difficult to do as I have him in a plastic box inside the tank. It's tough to shoot through glass as well as the plastic.
I will try again tomorrow.
It appears ulcerated. I had noticed a mark in that spot before, but it looked like a scar or something, i.e., perhaps a cut in the scales that had healed up but with a cosmetic flaw. It didn't look anything like it does now.
He has been in a 90 gallon tank for several months, since I got him. It's tough to get a close up view of him in the 90. I just moved him into a smaller tank (34 gallons) today. I moved him, and then left the room for about 10 minutes. When I moved him, I noticed the mark on his head.
I came back in the room and he was nowhere to be found. At first I thought he jumped out of the tank, as he just disappeared. After about an hour of searching, I finally noticed some dirt coming off some live rock, and he was attempting to burrow himself into a hole in the rock. I have never seen a clownfish do anything like this, so I got him out and put him into the plastic box so I could watch him and so he wouldn't go back into the hole where I would be perhaps unable to get him back out.
He is swimming around slowly but otherwise acting pretty lethargic, definitely not the normal clownfish action.
He's been eating fine in the 90.
The 34 has new saltwater as of last Saturday, and the live rock came from the 90. Temp and salinity were the same in both tanks.
Two other clowns are acting perfectly normal...