I think that due to poor genetics similar to PLJ. Ive seen some of those humped back aros in big tanks with 3’ wide and in some silver aro that are short body. Not saying it cant happen tho.I've seen stunted ones returned to fish stores that came out of tanks roughly that size. Humped backed and looking very pityful.
Op
You are going to be more than fully stocked with the stock you already have.
Forget the arowana.