A submersible rotatable cage for fish farming comprises a central axle, a buoyant structure positioned about the central, a netting attached to the buoyant structure and an actuator in operable communication with at least part of the buoyant structure and adapted to facilitate rotation of the buoyant structure about the central axle while the cage is in a submerged position. The cage can form part of a system, which includes a net cleaning apparatus, a tethering mechanism and sweep net, that can be used for nearly complete underwater fish farming.