P. Brachyura get 3 feet across and have yet to breed in captivity from what I've read.. They are very different than most other Potamotrygon, and would be more suited to be grouped with Paratrygon (ceja) and Plesiotrygon (antenna).. They are much like the small-eyed rays with their finicky ambush predation feeding habits..
A ray you don't see very often, and if you have a link I would like to ask the guy about it.. They only come from Brazil and Argentina.. you know it's not coming from Brazil, and not many people import from Argentina, unless on a large-scale commercial basis..