Just kidding, For bigger fish I've used pillow cases, platic bags, trash bags, and the really big fishing nets they sell at Dicks Sporting Goods. (not the ones made out of nylon but the rubber ones)
Barramundis are a bastard to net. When you use one of those fine meshed nets anyways. They have razor sharp gills which stick into the net and get the fish caught in the net. So when handling Barra, don't use fine meshed nets, lol.
it's easy get the biggest net you can afford and go for it. make sure you open a tiny gap first so the aro don't jump out. once your net is inside the tank force the arowana into one side. if the aro freak out then back off, then do it again. give it about 15mins with the net in the water, the aro will get use to the net by now. then with out warning net the slippery thing out! oh, and it's best if you can get some one stand next to you so they can help you open the box, past you stuff etc.
and four hands are better then two when it comes to catching fish lol.
heavy duty plastic bags. the kind they ship fish in. if need move it long distance, place the bag in a container (such as styro/plastic box) of similar volume as contents of the bag. Helps to double bag and slide news paper in between so that the fish cant see what's going on.