kribensis keeper

one of my zebra danios has a thing kind of like a hole on his body but it looks that his scales have scratched off but it is a little bit deep i guess you could say its deeper then a graze and it is bulging out a tiny bit on the oppisate side of the hole on the other side of his body what is it? he is eating a little bit and is swimming fine just not as active as the other danios and his fins are not clamped. could this be a diseas or has he just scratched himself i don't want any of the other danios of fish to get it if it is a disease please help. could it be that disesase that is mainly known in danios

please please help

Tony G.

hmmm... is the scale raised?
does he look to be bleeding?
are there any small ornaments/deco he could have gotten himself stuck in?
have you introduced any new fish recently?