Wait...did someone put an Oscar in a 33g tank? WTH
Minimum recommendations for an Oscar is 55. That stated...I have an Oscar, and just moved him from the 55 to a 75, because I thought it might be too small in the long run. His tankmate is a pleco....and that's it.
No, there are no rules, only quality of life. Yes, a person can live in a single room apartment, but how comfortable is it? Me

I moved after a year. :P I would no more want to live in that apartment again, than I would want to put an Oscar in a 30g tank.
IMO, that should be considered animal cruelty.