i think i have to cancel the choice of keeping an oscar...
are there any fish that are personable and inteligent as oscar, but require less spaces?

there are several differnt new cichlids that can be housed in a 50. jack dempseys, firemouths. severums, this list is quite long. however if you are willing to do the work involved(water changes) you could keep a single oscar in a 50 for a while while you shop around for a larger tank. just a thought

i can't really keep a tank which is more than 50 gallon...
is ja dempsy a personal fish? i like fish that interact with me as oscar.

i dont think anything is a personable as an oscar but my jack is most enjoyable,(when he's not picking fights with my other fish) they can be a little aggressive but a 50 should be enough room for a pair of them(male and female of course)

i just checked that jand dempsy also needs a 55 gallons minimum

i am keeping a male and a female jack at this time and i am planning on housing them i a 55 gallon tank. its true that a 55 is the minimun for a pair of jacks however they do not grow like oscars do. my male jack is about a year and a half old now and he is only about 7 inches in length. they are not the same as o's when it comes to bioloads either. until recently i had the pair in a 30 gallon tank and just recently moved them because it was gettting a little crowded. even in the 30 my nitrates in that tank never surpassed 40 ppm and they are both healthy and happy. also for the record when looking on most websites for tank size they usually give in american gallons not imperial gallons.