Ive kept guppies and mollies in with my red eyes and green tree frogs for about two years with no problems, they actually bred like mad, but like mentioned above you will most likely lose a few as frog food so don't get expensive ones and you will need a good filtration system to keep up with both the frogs and fish, I hide a stocking with a couple hands full of fish tank charcoal under the gravel as well to help keep it clean