Stuart is very knowledgeable, spent 3 weeks at his places, and can be contacted through the Ask Stuart section on his website or via e-mail.
When i was out there i was told that as soon as the arapaima jumps to drop the rod tip otherwise they have a habit of shaking the hook. But in the end i found that an even better way was to play them using sidestrain as much as possible as this stopped them jumping altogether as they can't use the tension in the line to help get them airbourne. With side strain they tended to roll on the surface instead and i lost far fewer fish, and i know that other people that i told to try this had better results as well.
You will always lose a few though as they feed by inhaling the bait and there is a tendency to hook them around the face which often results in a hook pull shortly into the fight.
They feed by dislocating there jaws for a fraction of a second when they inhale the bait, but the rest of the time they don't open that far. This means you have to be careful unhooking them as if you force their mouth open too far it snaps the muscle and they can't feed so die - best to cut the line if in doubt.
To help prevent them swallowing the bait it is best not to freeline, either float fish or use a method feeder or sunken bubble float to stop them taking it back too far.
Deadbaits and livebaits both work, but the smaller the better as it is easier for them to inhale. Hit bites straight away as they either have it in their mouth or they don't, they're not like pike where you have to wait for them to turn the bait.
The most important thing is when handling the fish not to bend their back. They are air breathers and have a blood vessel running the entire length of their back and if bent this snaps and they bleed to death - hence Stuart using cages to land them in and at least 3 people to lift the fish for a quick photo in the water.
When releasing them Stuart discovered that you need to make a big splash to make them think another arapaima is close by and make them bolt off, otherwise they go and sit on the bottom and can forget to come up for air and die.
There is always a chance of having one die on you, but Stuart loses very few compared to other waters and this is a risk you have to accept if you're going to fish for them - you just do as much as possible to prevent it happening.