Syn, bifa, hartwegi and fenestratus all look very similar as juvies.
I don't think syn because of the amount of blue I see and also the length of the black lateral line on the body.
Could be a washed out bifa - I see a small amount of black on the upper half of the body. Looks like too much blue in the body though. Bifa usually are more gold. Could very well be a bifa though.
Its the amount of blue I see in the body of the fish that makes me think fenestratus or hartwegi. Thats assuming of course that the fish is not a vieja hybrid.