http://imgur.com/a/WTmOD#1

One of my male rats has these mini scabs all over his back. I'm trying to figure out where they came from. Could they be fighting at night? The rat he's with (not shown) is his brother and have been with each other since birth, so I don't see why they would fight. Or is it some kind of sickness? I've never seen this on any other rat.