I get mixed feelings on this from a lot of people Alpha 7. The minimum tank size in my opinion and experience for an oscar to live a long "normal" life would be a bare 55. Let me explain. If the tank is bare it's very easy to vacuum up poo or uneaten food when you do you water changes. If the tank is bare it's easy to provide you oscar with "things to do" like ping pong balls or practice balls from your golf bag. Heaters are not necessary once the oscar matures so you don't need to worry about the oscar breaking your heater... Now the major one I often get "Keeping a 14" fish in a 12" wide tank isn't going to work" MY answer to that is consistently the fact that fish are flexible, they can definately turn around just fine, they're not torpedos or submarines. The singe oscar quaetion is easy for me to answer, it's keeping multiples that gets tricky. I've got 95 oscar fry in a 50 breeder. Six of them will be moved to a 125 to eventually pair off. Once I get a pair the others will have to be removed, until then it's going to be a very interesting and fun tank to watch and care for.
To anyone wanting to keep more than one oscar I'd suggest they do the same, if not it will more than likely end in disaster.
fishtycoon11/Jeditwin, The fact that your juvi oscars swim together and never leave each others side is because it's their instinct to school for survival. Once they mature the dynamics of the tank will drasticly change.
My first cichlids ever were two Oscars in a 125. When they were juvies they seemed like best friends i was hoping they would pair off and breed, then when they grew up they were both angry males that would stay away from each for a while and then fight so hard they shattered a glass heater (rookie mistake, shoulda been plastic.) broke a hood and ripped the intake's off two filters. They had to be separated.
Mature cichlids, the robust ones like oscars, texas, midas, synspila, JD, GT do not need heaters when older. The only reason a heater is necessary is if you want the fish to spawn. Most people just keep the heaters in as a disease preventative. Most of my tanks are not heated... Especially in summer. Ever been to a fish show? Only a few tanks are heated, those being the discus and the fish with paranoid owners... And remember we're talking fish that sell in the hundreds of dollars range...