The quick evolution of fish farming in Europe, and its development towards the open sea needs suitable farming tools. These tools must withstand the difficult sea states, but they must be easy to use, well adapted to the fish farming and not too much expensive. This book helps the design of such tools. It defines the solicitations of the sea on all the structures, and presents rules and methods to control these solicitations. Here, a structure is composed of a rearing support, a mooring system and equipments. This book describes these components, class them and gives lists of providers. The rearing support can be a cage, a group of cages or a boat. The support can float or to be submersible. The mooring system can be made up ropes, chains, anchors, concrete blocks, floats, clump weights... Equipments are all these tools as manual-automatic feeders, graders, aerators, sensors, fish pumps, net washers, antifouling, nets, net cleaners, counters, scales, work boats... In this book the environment of the fish farming structure is: the atmosphere, which takes into account the wind, the corrosion and the dissolved gases, the sea water, which is the main vehicle of solicitations, as wave and current forces, tide effects or corrosion, the sea bottom, where the structure is moored through the foundations of the mooring system.