another option is to find someone who would take them in when they reached a certain size. or you could even setup a good sized pond space permitting. ive seen "ponds" that i was looking into about 600 gallons for about 800 dollars. but yet they claimed the shipping to be as much as the pond itself. it was more of a stock tub, but it would do the same trick.
not trying to discourage you from having an arowana, but they need their space to thrive.
not trying to discourage you from having an arowana, but they need their space to thrive.