There are three types of purely aquatic frogs that you'll see commonly in the aquarium/reptile hobby.
-The Dwarf African frog, which are timid and should be kept with very peaceful fish
-The African Clawed frog, which is bigger and mean, and goes with semi-agressive fish big enough not to fit in it's mouth.
-The Pipa Pipa, or Surinam toad, which is the biggest at 6+ inches and good with big peaceful fish (I had mine with arowana and similar).