[akiselev]

The vast majority of the energy in the food chain of a body of water comes from the sun so the bigger it becomes, the more volume of water there is relative to the surface area exposed to the sun. You can try to multiple the number of fish by the number of aquariums that would fit into a lake but the vast majority of those fish would starve competing for the limited amount of energy coming hitting the surface.

[polycaster]

Thanks for pointing that out. Moving away from skyscrapers you could still successfully scale in 2 dimensions? Which I assume is what fish farming is primarily about, right? Depth brings more limitations like pressure, behavior of gases etc.