Freshwater Altantics are a prolonged death unless you have them in a tank 10 times the volume (or more) of what they would need as marine animals, and have them acclimated correctly.
That being said, Fl has banned all freshwater rays. Keep saltwater species. There are several that stay small and are very hardy. Yellow, Round and Cortez are the biggest three I suggest going with for a starter ray.
Why are so many people affraid to make the jump to keeping marine rays in areas where they can't have freshwater species??
If someone were to have any of the South American rays in a private collection, those would be illegal. After extensive talking with FWC on the topic over the past month or so, I can assure you they will not and have not ever granted permits to private owners.