that is a very large tank (roughly 150 gallons). You can put more than once oscar in the tank. possibly up to 4 once full grown. other than that your tank is so large that you can put any fish in it. i would though keep in mind that though you still have a large tank be careful what fish you do buy and keep in mind the sixe they are when they are full grown. my favorite fish besides a saltwater aquarium are cichlids. oscars are in the cichlid family/ however african and south american cichlids are more aethetically pleasing:http://www.aquaticcommunity.com/cichlid/