That pattern and body shape looks almost identical to a ray we own that came origionally from H20 Custom Aquatics (I got it from Miles). She (her name is Molly) is part of a trio of rays that were labelled Marble Motoro / Mantilla hybrids.
The strange thing about the trio is the stark pattern contrast between the two males (who are extremely colorful) and the female (who is the beautiful cream color depicted in your photo above).
So, tenatively I would say that it is a mantilla ray of some sort. Species identification is so difficult for many species of Potamotrygon stingrays, but it definitely is from the Potamotrygon genus.
Beautiful ray!