Variety of technologies
The systems and technology used in aquaculture has developed rapidly in the last fifty years. They vary from very simple facilities (e.g. family ponds for domestic consumption in tropical countries) to high technology systems (e.g. intensive closed systems for export production). Much of the technology used in aquaculture is relatively simple, often based on small modifications that improve the growth and survival rates of the target species, e.g. improving food, seeds, oxygen levels and protection from predators. Simple systems of small freshwater ponds, used for raising herbivorous and filter feeding fish, account for about half of global aquaculture production.
A greater understanding of complex interactions between nutrients, bacteria and cultured organisms, together with advances in hydrodynamics applied to pond and tank design, have enabled the development of closed systems. These have the advantage of isolating the aquaculture systems from natural aquatic systems, thus minimizing the risk of disease or genetic impacts on the external systems.
Developments in engineering, some adapted from offshore oil rig construction, increase the possibilities for a progressive offshore expansion of aquaculture using robust cages. Culture-based capture fisheries involving the release of young fish into the wild to improve harvest (an operation also referred to as restocking, stock enhancement or ranching) have existed for a long time for freshwater and anadromous species (e.g. salmon). Sea ranching, however, has just made a start but its long-term viability is being assessed. Advances have also been made in capture-based aquaculture involving the growing/fattening of young fish (e.g. tuna) captured from the wild. Potential conflicts with capture fisheries are being assessed. Major progress have also being made in the aquafeeds technology, combining a large number of ingredients into very small pellets.
The selection of the aquaculture system or approach to adopt in a particular development is determined by several factors including the following: