Strange question?

[bushwhacker]

not to mention you need the surface agitation for o2 exchange

 

[jpappy789]

not to mention you need the surface agitation for o2 exchange

Not necessarily. In a heavily planted, low stock tank the plants will produce enough dissolved O2 for the fish and in exchange the fish produce enough Co2 for plants...but this is all in theory, and such a balance is hard to obtain.