well...i guess this aint gonna help much but my friend has a very large tank, maybe 500+gallons, and he has like...the trunk of a tree going down into it and coming out of the water, and in the tank he has a huuuuuge red tail catfish and a pretty large turtle. Ive never even seen the turtle get up on the tree trunk though...
oh well. but yes, like they above said, i doubt you'd be able to house any small fish with a turtle.