This type of aquaculture system requires the least amount of inputs and maintenance, and therefore has lower operating costs. However, such systems tend to have higher environmental impacts and a higher occurrence of disease or parasites. Nevertheless there are many farms utilizing extensive systems that produce safe and delicious products.
- Pond Farming involves fully growing out fish in open systems, which can be highly susceptible to water evaporation, uncontrolled inputs, and inefficient feed conversion. Output is typically lower than more intensive systems, and there tends to be higher environmental impacts. However, the cost of production is kept low, making pond farming most feasible in less affluent countries or communities.
A step above extensive systems, semi-intensive aquaculture systems receive higher levels of inputs such as purifed water or specialized feeds, which result in more efficent seafood production than extensive systems. These are the most common type of systems in the United States, and while there are criticisms such as the high water demand, there are many sustainably certified producers.
- Flow- through systems are among the most common production methods for aquacultured seafood, and work by allowing water to flow, either via pumps or gravity, through the system to supply food and oxygenated water to the animals and whisk away waste products. With these systems, there is minimal treatment to the effluent waters, and they are generally water intensive. However, technology such as water coolers and better feeding mechanisms can be applied to these systems to minimize water loss, superfluous water discharge, and to increase biomass production efficiency. Examples include land based raceways and tanks, and cages or nets in waterways such as canals and streams.
- Nearshore cages are often utilized in coastal waters to grow finfish while ropes and lines are utilized to grow shellfish and other invertebrates, as well as vegetation such as seaweed and kelp. These systems utilize natural waterways and currents to supply the animals with fresh water flow, remove waste, and provide the organic and inorganic materials needed for healthy growth of the products.
Considered the most demanding and expensive systems, intensive aquaculture systems use purification processes and specially designed feeds to maximize biomass output and quality while minimizing environmental impacts.
- Recirculating Aquaculture Systems (RAS) are among the most recent scientific aquaculture advances, and further research is being implemented to make RAS cost effective. These systems use filters and purifiers to clean the tank’s water, which can then be recirculated back into the tank, dramatically reducing the amount
of water required to grow the fish. It also allows for more controlled disposal of waste products. Land based tanks utilizing RAS can produce more biomass in an efficient and environmentally sustainable manner.
- Open Ocean Cage Systems reduce environmental impacts through the dissolution of waste. Located further offshore than the more common coastal cage systems, open ocean cages allow for waste to be carried away with strong currents, preventing accumulation of organic matter and many of the environmental issues that result from it. The strong currents also supply the cages with consistent oxygenated water and help squander disease by providing a constant flow. The operating costs of these deep water systems, not to mention the deterioration of the cages from saltwater and weather events, make this type of farming more expensive and labor intensive than smaller land based systems. But it is growing in popularity due to its reduced environmental impact.
- Integrated Multi-Trophic Aquaculture (IMTA) Systems take advantage of the outputs of one aquaculture operation of a higher trophic level, such as carnivorous finfish cages, to supply the inputs for a lower-trophic level aquaculture operation, such as shellfish or plants. This design maximizes the potential of its outputs, producing the highest biomass possible, reducing costs, and minimizing negative environmental impacts. An example of IMTA is an offshore cage for snapper located up current of oyster beds that can utilize and filter the organic matter runoff from the finfish, which are followed by seaweed strands further down current to uptake any remaining inorganic materials.