Well, we take fish that, during the normal course of a day in the wild, would swim constantly and likely cover many acres of space cruising around looking for food and avoiding predation. We stick them into a "big" tank that's a few feet long and wide and watch them swim around in circles. They bang into stuff and freak out a bit...and during the freak-out they smack into a few more obstacles, which escalates the panic and it gets out of hand.
In nature, something that startles them results in a flip of the tail that sends them scooting a distance which likely is several times the length of their entire tanks in captivity. And a jump, which in nature would be a non-event, turns into a potentially dire affair in captivity; they jump, they hit the lid, they get more spooked, they go ballistic...and then they get hurt.
It only gets worse as they grow larger.
Unfortunately, it's just the nature of aquarium-keeping; something we try to minimize but must face. Also, Arowanas...and I think they are terrific fish...are not the saltiest crackers in the box when it comes to intelligence. All instinct, no brains. Startle or scare a cichlid and it knows all the hidey-holes in the vicinity and how to use them to best advantage; startle an arowana and it knows "Gotta GOOOOO!"
