Hi, this is definitely marbled motoro, i got this type also from my import. i also noticed some of the wild ray is losing their spot. this could be too close from the natural inbreeding. in the wild, it is hig chance for the inbreeding to happen if the ray is from a small river or lake.
as to my knowledge, Marbled motoro have a few type depends on where they come from, those type you have is probably come from Pto Ghaitan river. there are some from Orinoco river, which is bigger spot and light color pattern. much more simple pattern type.
I hope they turn up as very nice ray. marbled will change a bit, give them some time.