The two on top are rat tubs, with the growing girls on the left and the (now lone ) male on the right. Once they're breeding size, I'll give each girl their own tub like the one they're in now and the males (once I get a second male to replace the one I lost) in with them unless there are litters. Then the boys get their own tub.
For 'extras', I have a really big tub plus two smaller ones to use for rats or mice (since I still breed them as well).