I'm going with the yellow bullhead. Last summer, I went to a pond near my brother's house and caught what I thought was a tadpole. It turned out to be a yellow bullhead juvie barely 1". I placed him in my 20G for a little while and his size increased to about 3". At that point, I set him free back in that pond before fall set in. A very cool fish.
My nephew thinks it's a blast to have an aunt who regularly goes wading in streams and other bodies of water in the warmer months.