get a big pike cichlid, my guy is like a dog, i walk by and drop frogs in, he just hammers them down, he watches me when i walk towards him he begs like a dog its pretty awesome, and he lives in harmony with my big male red devil,
my devil is only in there when my female devil has fry so the pike is pretty good about sharing his space because there both super well fed, ... but my big devil male just beat the tar out of my male festae so hes in the hospital, key is no females
here is a vid before i added my devil and pulled the festae male http://www.youtube.com/watch?v=fR4s-ii3gu4
i will post one tonight when i feed the pike a frog or some tadpoles or something you will see he is just like a dog
If the guy is asking if an RD and Arowana can coexist well in a 55 gallon he obviously doesn't know much. You guess should not be encouraging him he probably has no plans for an upgrade.