OK ..first sorry MOD's I cant keep my mouth shut anymore.
89Must, I do not conform to most stocking recommendations but I have learned from experience 2 large oscars in a 90G, with a 10in Pleco, and two 5in Raphael catfish is to much, after the tank had been established the water conditions after 1 week would be over 60 on nitrates, this lead to the beginning of HITH, I took care of that, I still lost my largest Oscar to some other infection 2 months ago. I trust Miss dixie and I know her info is correct.
I will say that since I lost my larger Oscar the smaller one as gone to fighting with inanimate objects in the tank for amusement, so there may be some truth to the have 2 oscar statement, but NOT in a 55G.
The other comments from Jo3 is based on the fact the original poster here did in fact ask these questions BEFORE buying a fish, then disregarded the recommendations of every response, which is fine, but then to have someone come along and say small tanks are fine, go for it, is adding to the problem of irresponsible fishkeeping, which most of us are here to try to wipe out, yes it is a forum and it is up to you on how to take the recommendations provided but I doubt you will find any knowledgable oscar keeper recommending to oscars in a 55G tank.
We are all here to learn and I hope the newbies stick around and we can learn from each other.