I don't know what to keep in a 150 gal tank. I like arowanas and alligator gars but I knwo they can not be housed in any aquarium because they would be i humane and cruel. I'd rather stay away from cichlids. I was think about freshwater rays or some other oddball fish. I would like some kind of predator fish. I have bichir in another tank for temporary housing. I like plecos, catfish, unique fish.