aggressive behaviour?

Question
Hi! Last week I brought home a group of 5 male rats from my local animal rescue centre. All was quiet and peaceful for the first day or so but lately there have been several incidences of agressive behaviour from one rat towards another rat, and last night the rat who is getting picked on had acouple of minor bites to his head. It is always the same two rats involved.  One rat is always mounting the other rat or pinning him down. I know he is showing dominant behaviour but why only towards one rat who does not seem to be trying to take over as alpha male.? Do you think it is because they are in a new environment and he is enforcing his position and it will calm down or should I consider neutering the trouble-maker? I worry about serious injuries and I don't like to see one rat being picked on. Your opinion would be greatly appreciated.

Answer
I'm sorry for my delay getting back to you; I've had the flu.

I would separate them and yes I would consider having the aggressor neutered, however keep in mind this won't be an instant fix.. it'll probably be more like a monthly progression into a nicer animal, all in all. It may be easier just to keep the bully out of the community area, or with a buddy he doesn't have an issue with, as those two obviously had words somewhere along the line.