What freshwater rays are suitable for keeping in an aquarium?

I’ve been thinking about setting up a freshwater aquarium. I used to work in a pet shop a few years back and found myself absolutely charmed with the few species of freshwater rays they would sell. This store has long since gone out of business, and I’ve never seen any at the larger retail pet stores. So my question is this: which species are capable of being kept? What would a good set up for them be? What other fish or aquatic creatures (if any) can safely be kept with them?