Aquaculture facilities can be land-based, coastal, or open ocean and can focus on a single species (monoculture) or include a variety of species of both plants and animals (e.g. polyculture of scallops, kelp and sea cucumbers in coastal China). The design of any operation depends on the technologies associated with containment and the methods of feeding, breeding, disease control and other aspects of animal husbandry. As a consequence, the species chosen for cultivation often determines which technique to use.
Freshwater fish, such as carp, catfish and trout, are farmed in land based systems consisting of (1) raceways where water is pumped from tank to tank (or pond-to-pond) and discarded; or (2) recirculating systems in which recycled water is filtered to maintain quality. Some marine or brackishwater species can also be held in tanks as long as there is a natural and economic supply of salt water.
Most marine species such as salmon, flatfish and cod are kept in large floating or submerged cages, or "netpens", anchored to the ocean floor in coastal areas. In many cases, finfish are given commercial feed made primarily from marine fish, although there are some freshwater species such as catfish which are primarily herbivorous.
Prawn or shrimp culture facilities are found primarily in coastal areas, in shallow brackishwater ponds or in tanks. Although supplementary feed isn't necessary, growth is maximized through the addition of commercial feeds. In most cases, ponds are created by forming embankments in low-lying coastal areas. These areas are flooded and enclosed, subsequently trapping shellfish juveniles from coastal populations.
Mussels and oysters can be grown in cages suspended on or just above the bottom, or in long "socks" or ladders suspended from the surface. In addition, scallops can be ear-hung on lines or scattered on the bottom to be retrieved by trawling several years later. Because scallops, mussels, clams and oysters filter phytoplankton and other food particles from the water column, supplemental feeding is not necessary. Site selection for bivalve culture is critical, therefore, to the success of the operation because food must be supplied entirely by water currents flowing through the farm.
Seaweed such as Laminaria is grown in long rows suspended from the surface. Nutrients are supplied primarily from the surrounding water, although fertilizer can be added to supplement natural supplies of nitrogen and phosphorus.