I've actually kept an Oscar with a few Severums with very little aggression. The Oscar usually sees the Severum as little competition and leaves them alone. The Severums grow more slowly so your not overwhelmed with more bioload right away. If you choose this route, get the Severums a little larger then the Oscar so the Oscar doesn't pass them in growth to soon. With this setup you will need some strong filtration. Do not skimp here! You can start out with adaquate filtration for small fish when you purchase them and then add additional filtration as they grow larger. Be advised though, you will need very good filtration and you will need very good maintenance practices to keep South American cichlids. Oscars when not even fully grown can leave waste as thick as your fingers on the substrate. You cannot leave this stuff lying around in the tank, you must get rid of it. The key to keeping large cichlids is not overfeeding them, which can be difficult for some people because they are always begging for food. Keeping these larger cichlids can be very rewarding as they become like household pets and they also require much more keeping after like household pets do.
