while it is good to keep oscars in groups it can be difficult beacuse you need alot of space. 75 gallons for the first one and 30 to 50 gallons for everyone after that. the theory behind having groups of oscars is simple.... in group of six or more oscars in a tank you usually get one aggressive alpha, having six divides the punishment usually dished out by the most dominant oscar amongst the six other inhabitants....thus they have a better chance of survuval. however, what ive found is that all oscars have different personalities. mine for instance is a complete cream puff and doesnt bother any of my fish(even my other little oscar and my angelfish). on the other hand ive had some pretty nasty oscars as well so be careful.