3 weeks old rat are weaned rats which would be a HUGE size difference with a hopper mouse.
If you go from hopper mouse your next step up would be small adult mouse or adult mouse or small rat pup to rat pup.
Though my advice would be to stay with a similar size since your attempt is too switch than after a few successful meals upgrade the size.
Switching can be tricky and offering the same size might help with the transition.
Now here are some size ref for you
Those are rat fuzzies 10 days old on the large side they can be larger than hopper
Those are rat pup similar to adult mice to slightly larger at that stage they are 2 weeks old.
Reply With Quote