certainly don't belong in the same tank. Melanochromis johanni (electric blue johanni) is an African cichlid which requires hard, alkaline water. i don't know what you mean by 'yellow' ram but you're probably referring to the gold ram Microgeophagus ramirezi, a south american cichlid which grows to only 2 inches and will be eaten by an arowana. morevover, this is a very sensitive species and will do poorly in a 'new' tank. there are several 'Arowana' species: OsteogLossum bicirrhosum, African Arowana - Heterotis niloticus, Asian Arowana - Scleropages formosus. all of them grow to over two feet and cannot be maintained in a 55 gallon tank.