here's something for you to think about you freke lol, how do you know arowanas in the wild DON'T get DE? have you gone swimming with wild aros to verify that they do NOT get it?
stop questioning life about there posture, it happens. and for over 30 years of the fish being in the hobby everyone has always wondered. they've performed surgery for reasons i don't understand. they fish must be so uncomfortable and possibility of him losing his eye sight or maybe even dying. not worth the risk if u ask me. i love all my aros, all 3 of my silver arowanas HAVE DE and 1 has DE in BOTH eyes, i still love them more then ever.
only fish i own that doesn't have it is my leichardti, but lets see how long that last.
but on a serious note, i always thought of it as a survival evolvement. he has tankmates below him at all times in a home tank, and the tank is so small he would have to kinda keep an eye on them to make sure he's safe. so over time his eye slowly starts to look down in a form like now he can see up, and down lol