So it cannot be Perrunichthys perruno.
I have no idea how to tell between Leiarius marmoratus and Learius longibarbis. They are very similar and have been only very recently separated into two distinct species and one has to read the sci paper that describes their distinction. Longibarbis is so new there are no pics at all in the Cat-eLog on PCF.
So for all intents and purposes, I'd propose it is a Leiarius marmoratus, a well known fish with a well known and much described care.