i used to feed large goldfish to my arowana for breakfast if that gives u any indication. plus even if it is too big to eat the arow would still kill it by biting chunks of it. so yeh no go!
a 20" silver aro huh.
I have seen my six inch jardini swallow a 1"+ barb after playing with it for nearly an hour or so.
here are a few pics.
(sorry for the quality of pics as all i have is my phone to shoot snaps)