And if you haven't added anything to the tank in 16 months, then I can assume the neon is at least that old and surely a bit older. Sometimes as fish age they just get strange growths. The fact that the neon is eating and behaving normally tells me it's not one of those illnesses that is going to affect others but more than likely something in its genetics that is happening with age. Some fish age faster than others, neons don't have terrifically long lives to begin with. Just more thoughts for ya!
