I was looking at frogs found in my area, because i am a nerd, and i thought of this thread. There is a frog that looks very similar to the bullfrog but it has ridges along its back and it only grows to about 3 to 4 inches. I looked up tadpole pictures and i cant tell the difference from these to bullfrog tadpoles. since your tads are smaller you think these could be the frog? I am no expert tho and would really ask john and Kurt about it. It also may help if i knew where you got the tads from.