Unless there is a breedable female around most times male rats don't seriously fight with each other especially if they are litter mates or are used to being caged together on and off. Our adult breeder male rats go in and out of the male only tub to breed and the most I generally see on their return is a bit of a boxing match, they get tumbled over and well sniffed and get that look from the other male rats "oh what have you been up to?" LOL Usually within a day they have fit themselves back into their place on the social ladder of rat life.