if u have to have a arowana, i'd go with a silver. not everyone realizes they have the most sleek and easy to turn around body design. jardinis and leichardti's have stiff bodies compared to silvers. even tho they get bigger, then can get by.
of course it aint right, but my friend grew a silver aro in his 80gal 20" wide tank for 4.5 yrs and grew it to 27 inches. i do not see this happening with a jardini. deforimty will be a guarantee