Oscars become aggressive when they are hungry. Otherwise they are more of a mellow cichlid.
To the OP, if the oscar is becoming a problem. Pop him in the 30g until your 300g arrives then reintroduce him with the rest of the fish. If you think he may be lonely, pop in one of your larger fish that wont be bullied. This way you are reducing the aggression and bio-load in your 'grow out' tank!
To the OP, if the oscar is becoming a problem. Pop him in the 30g until your 300g arrives then reintroduce him with the rest of the fish. If you think he may be lonely, pop in one of your larger fish that wont be bullied. This way you are reducing the aggression and bio-load in your 'grow out' tank!