The gator gars imo are gonna be the biggest threat.. not only are they the largest Gar species but notoriously aggressive in captive tanks.. getting some spotted/florida gars might work for you. If you pop over to the gar section you can get some very good info, and see what you're looking at if you decide to keep the gar. a Gator gar can and usually will get 24" it's first year. a 200Gal wouldn't hold it for very long.