The two general types of cages used in offshore aquaculture are floating or submersible. Floating cages are square, octagonal or circular, and are constructed from a variety of materials. These use an internally-hung net pen for fish culture, and a separate, externally hung heavy-duty net designed to exclude predators. The cages are constructed with metal couplings, plastic or rubber pipes, polyethylene floats, sheet metal, metal tubing, or some combination of these components.
Offshore aquaculture technology also uses large submersible cages to grow fish species, and they are anchored on the sea floor. These are able to move up and down the water column. The cages have buoys attached to them on the surface and these have a mechanism for feeding and storage. Offshore waters have multifunctional uses, thus making aquaculture even more sustainable.
Integrated multi-trophic aquaculture or polyculture is another sustainable ocean farming technique where species like finfish that must be fed are cultured alongside species that can feed on dissolved nutrients. This method is being pioneered in Spain, Canada and elsewhere. The ‘next generation technology’ envisioned for offshore aquaculture is Roaming Cages in the form of large mobile cages powered by thrusters and able to take advantage of ocean currents. It is a concept designed to take fish species from one country to another in mobile cages in a period of months, where they will be fully grown by the time they reach the final destination.