I keep 1.2 mice per tub (26x15x10) together all the time. I just got a sweet trio of rats (Thanks to Fearless! ) and I keep them in wire cages since my previous tub attempts with rats were disastrous. The girls live in a 2 story cage together and the male has his own single story cage. Once breeding and the girls are close to delivery, they each have their own 10g tank.