i've a problem to specifiy this fish:

It`s not an specified Otocinclus and i'm not shure if this could be a Otothyris lophophanes. Can anyone tell who to classified this fish?
This fish is over 4 years old, the white pigmentation on the front will be more brightly when he gets older.
I don't know the place where they catch this fish.
Thanks for any hint.