Quote Originally Posted by harm286 View Post
You kno some stuff man. So let me ask you something, is keeping two male rats and two females in a tank a bad thing?
Not always, but I don't recommend it.
Males might fight, or you will end up with a dominate male and a submissive male that is doing nothing but causing stress in the group.
Males sometimes(quite common) get scratched up during the mating, and then afterwards too when he won't stop mating, even if she's preggo.
If he isn't too aggressive, it's ok to leave him in, I've left males in and had no issues.
I've even got great joy from watching males curl up with almost weanlings for naps, very cute stuff.

That said, I now remove all of my females to their own space to have the babies, since I don't want my females getting pregnant while nursing.