no, its not like that, i mean the mom and pop shops just buy a whole bunch of mice and they just breed like crazy, there is like 6 different tanks all with a different variety, a whole bunch of small mice, in another tank u have some big ones and small one, a bunch of pinkies everywhere, there not very organized, but the ones i see that seem to be that perfect size and weight, always are "pregnant" or something like that, either that or they are too big, i was at petland the other day and i saw a small "rat" that seemed like it would do the job, but i dont want to give him something too big, or something hell wont take maybe. Today is feeding day and im going to try the mom and pop shop again, and see if i can find something perfect, but its like everytime i go i just end up making the same descision and asking them to give be the biggest they can find in the small mice tank, which ends up being just liek 35g give or take....