Sore by Nostrils on Orangethroat Darter

I've had the orangethroat darter for several years now and a week or so ago an area of flesh appeared near it's nostrils that seems to have lost some scales. It seems like it might be growing in a size and I'm a bit concerned for the fish's health. It still moves around and eats, but I'm worried about the risk for infection. I haven't added any new fish to the tank in several months so I can't imagine anything has been introduced. It moves around a lot so I've had a tough time getting a photo. Any suggestions as to what this might be?
Or is it anything to be concerned by at all?

Can't see any pic, but it sounds bacterial in nature, and bacteria can spread through the air.

Age may be weakening his immune system, allowing bacteria that he's lived with for years (without symtoms) to take hold. The nasal infection could be from many possible causes, but Mycobacterium is one that seems to "specialize" in slowly killing older aquarium fish.

Hmm, I have some 6 year old logperch that recently started having red nostrils. I wonder if that's what it is.