i have never seen or done this before, but with careful planning i cant see why not.
there are a few things to think of....
1. you will have to have very good filtration to keep water clean, dont want your frogs soaking up any amonia, nitate, nitite ect
2. tree frogs are not great swimmers so water would have to go on a slow gradiant from shalow to deep, in the deep there should be rocks or wood breaking the water surface, so if they do get into trouble they can climb out and jump to safty.
3. what fish would you keep, dont want anything that may attack frog when he goes for water.
4. how tall is your tank, tree frogs like to climb and need height, however darts like space to move around at ground level.
5.frogs reales toxins through there skin(especially darts) so you would need to find away of stopping this killing the fish.
if you want fogs and fish there are a few species that are fully aquatic!
Hope this has helped
