We had rescued 100+ silver arowana in the past 15 years but this has been a first. This fish developed positive buoyancy and totally lost balance in about 6-8 hours in the new 4500 gal tank for no good reason that I could see, and then died 2 days later in isolation tank, where it was alone, having never recovered normal buoyancy.
Aussia the 3.5yo rescue arowana of Austin and Asia's has been seemingly trying to make up for the lost time by feeding exceedingly greedily and gets upgraded to 1800 gal: