1 oscar in al 20 gallon(75 liter) and its bigger as his hand.
its a shame..and u got a 55=200liters(also to small for a oscar but ok,,he can turn his ass in the tank...did u never say to ur neighbour,,that his tank is to small??
in my 20 gallon ive got little 2"nigrofasciatums 1 couple,an a few small corydoras,,
the minimum for a couople oscars is about 150 gall..because they are big eeaters,,lots of proteine in the tank,, and its nice they can swim as well