Hate to tell ya, O's get bigger than that. Mine was a hair over 15 and still growing. Others here have had 14 inchers. They can max at 18 but are usually old in gigantic public aquariums.
For a 125 you could try
1 O and two parrots
or 1 O, one parrot and one acara
+ A few danios if you want fast smaller fish to mingle (likely snacks but some might escape or be left alone)