Okay here is the trick I learned on my last, large arowana move.
I drained the arowana tank until there was about 6 inches of water left in it. I then netted up all the other tank mates except the arowana. I then used a large heavy duty black trash bag and placed it in the water at one end of the tank. After a few minutes my arowana excepted the bag in the tank and I was able to coax him inside the bag with a small net. I closed the bag and picked him up, and presto it was all down hill from there. After I released him into his new tank I observed very little damage to him.