It seems like now would be the time to do something. Could it heal and be just fine with it protruding? Seems like it's in a lot of pain. Thrashing all night. Does it need to be put down?
What I would do if I were you is seperate the fish immediately. Put the arowana in a seperate tank. Treat him with salt or melafix and heavily airate the tank. You might also want to use pimafix to prevent the wound from becoming infected or growing fungus. Depending on how bad the wound/bone sticking out I would possibly try and apply a liquid bandage of some sort BUT only if it's placed in a seperate tank that is heavily airated.sedate the fish first. try to push the bone back in place before the liquid bandage/adhesive is applied. I've heard of this process being done with expensive and high end koi fish but have never done it myself so Research the topic a bit yourself I'm not sure what types of liquid bandage are safe or not.best of luck and please post pics, water parameters, and any other info you think may be helpful.
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Don't you think netting the aro Would cause a lot more stress and possibly further damage?
any update on this fish?