Arowanas are neat,but require along tank with a very secure lids they are jumpers.some animals that have ben requested are a good choice for that size tank.but if you are upgrading the aquarium and like large cichlids...I myself love most central & south american cichlids! I have kept and breed two species. Besides that any better to me would be freshwater stingrays they are epic! if you do choose larger cichlids try an electric blue jack dempsey or a red terror fastae there colors are amazing for a fresh water fish.I'll post some pictures on my photobucket and share them soon.