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It currently contributes nearly 50 percent to global food fish supplies and is expected to continue this contribution in the decades to come and to improve food and nutrition security globally. However, as the global population is growing at an alarming rate and there are expected to be nine billion people on the planet by , maintaining the level of consumption of aquatic food could become an intimidating task.
In the recent past, aquaculture has shown its potential to generate important benefits to society and to contribute to the well-being of humanity. With an 8 percent annual growth rate over the past three decades, aquaculture produced 73 million metric tones worldwide in , which represents 39 percent of the production volumes produced from both aquaculture and capture fisheries. In , aquaculture brought about billion USD to the world economy, which represented 53 percent of the total value of aquatic products that year.
Yet, as a young industry, with globalisation aquaculture has become an international and complex business operating in many countries and involving many species cultured under different farming environments and systems, using different technologies and targeting different markets. Asia has retained its progressively dominant position in world aquaculture production accounting for nearly 90 percent of world aquaculture production by quantity and nearly 80 percent by value.
China alone accounts for about 60 percent of world aquaculture production by quantity and about 50 percent by value. Growth in aquaculture production is not uniform among the regions. China overwhelmingly dominates the world in reported aquaculture output,  reporting a total output which is double that of the rest of the world put together. However, there are some historical issues with the accuracy of China's returns. In , the fisheries scientists Reg Watson and Daniel Pauly expressed concerns in a letter to Nature , that China was over reporting its catch from wild fisheries in the s.
Watson and Pauly suggested this may be have been related to Chinese policies where state entities that monitored the economy were also tasked with increasing output.
Also, until more recently, the promotion of Chinese officials was based on production increases from their own areas. China disputed this claim. Mariculture refers to the cultivation of marine organisms in seawater , usually in sheltered coastal or offshore waters. The farming of marine fish is an example of mariculture, and so also is the farming of marine crustaceans such as shrimp , mollusks such as oysters , and seaweed. Channel catfish Ictalurus punctatus , hard clams Mercenaria mercenaria and Atlantic salmon Salmo salar are prominent in the U.
Mariculture may consist of raising the organisms on or in artificial enclosures such as in floating netted enclosures for salmon and on racks for oysters. In the case of enclosed salmon, they are fed by the operators; oysters on racks filter feed on naturally available food. Abalone have been farmed on an artificial reef consuming seaweed which grows naturally on the reef units. Integrated multi-trophic aquaculture IMTA is a practice in which the byproducts wastes from one species are recycled to become inputs fertilizers , food for another.
Fed aquaculture for example, fish , shrimp is combined with inorganic extractive and organic extractive for example, shellfish aquaculture to create balanced systems for environmental sustainability biomitigation , economic stability product diversification and risk reduction and social acceptability better management practices. In this case, these organisms may all share the same biological and chemical processes, with few synergistic benefits, which could potentially lead to significant shifts in the ecosystem.
Sometimes the term "integrated aquaculture" is used to describe the integration of monocultures through water transfer. Aquaponics , fractionated aquaculture, integrated agriculture-aquaculture systems, integrated peri-urban-aquaculture systems, and integrated fisheries-aquaculture systems are other variations of the IMTA concept. Various materials, including nylon , polyester , polypropylene , polyethylene , plastic-coated welded wire , rubber , patented rope products Spectra, Thorn-D, Dyneema , galvanized steel and copper are used for netting in aquaculture fish enclosures around the world.
The farming practices and economics of aquaculture in Thailand | WorldFish Publications
Recently, copper alloys have become important netting materials in aquaculture because they are antimicrobial i. By inhibiting microbial growth, copper alloy aquaculture cages avoid costly net changes that are necessary with other materials. The resistance of organism growth on copper alloy nets also provides a cleaner and healthier environment for farmed fish to grow and thrive.
If performed without consideration for potential local environmental impacts, aquaculture in inland waters can result in more environmental damaging than wild fisheries , though with less waste produced per kg on a global scale. If non-local live feeds are used, aquaculture may introduce exotic plants or animals with disastrous effects. Improvements in methods resulting from advances in research and the availability of commercial feeds has reduced some of these concerns since their greater prevalence in the s and s.
Fish waste is organic and composed of nutrients necessary in all components of aquatic food webs. In-ocean aquaculture often produces much higher than normal fish waste concentrations.
The waste collects on the ocean bottom, damaging or eliminating bottom-dwelling life. This has been used in the "ranching" of abalone in Western Australia. Tilapia from aquaculture has been shown to contain more fat and a much higher ratio of omega-6 to omega-3 oils. Some carnivorous and omnivorous farmed fish species are fed wild forage fish. Although carnivorous farmed fish represented only 13 percent of aquaculture production by weight in , they represented 34 percent of aquaculture production by value.
Farming of carnivorous species like salmon and shrimp leads to a high demand for forage fish to match the nutrition they get in the wild. Fish do not actually produce omega-3 fatty acids, but instead accumulate them from either consuming microalgae that produce these fatty acids, as is the case with forage fish like herring and sardines , or, as is the case with fatty predatory fish , like salmon, by eating prey fish that have accumulated omega-3 fatty acids from microalgae.
To satisfy this requirement, more than 50 percent of the world fish oil production is fed to farmed salmon. Farmed salmon consume more wild fish than they generate as a final product, although the efficiency of production is improving. To produce one pound of farmed salmon, products from several pounds of wild fish are fed to them - this can be described as the "fish-in-fish-out" FIFO ratio.
In , salmon had a FIFO ratio of 7. In , 34 percent of fish oil and 28 percent of fishmeal came from residues. As the salmon farming industry expands, it requires more wild forage fish for feed, at a time when seventy five percent of the worlds monitored fisheries are already near to or have exceeded their maximum sustainable yield.
An important step in reducing the impact of aquaculture on wild fish is shifting carnivorous species to plant-based feeds. Salmon feeds, for example, have gone from containing only fishmeal and oil to containing 40 percent plant protein.
Another impact aquaculture production can have on wild fish is the risk of fish escaping from coastal pens, where they can interbreed with their wild counterparts, diluting wild genetic stocks. Aquaculture is becoming a significant threat to coastal ecosystems.
About 20 percent of mangrove forests have been destroyed since , partly due to shrimp farming. Most of these farms are abandoned within a decade because of the toxin build-up and nutrient loss. Salmon farms are typically sited in pristine coastal ecosystems which they then pollute. A farm with , salmon discharges more fecal waste than a city of 60, people. This waste is discharged directly into the surrounding aquatic environment, untreated, often containing antibiotics and pesticides.
The Future of Fish Farming May Be Indoors
In , mass fish kill events impacted salmon farmers along Chile's coast and the wider ecology. Sea cage aquaculture is responsible for nutrient enrichment of the waters in which they are established. This results from fish wastes and uneaten feed inputs. Elements of most concern are nitrogen and phosphorus which can promote algal growth, including harmful algal blooms which can be toxic to fish.
Flushing times, current speeds, distance from the shore and water depth are important considerations when locating sea cages in order to minimize the impacts of nutrient enrichment on coastal ecosystems. The extent of the effects of pollution from sea-cage aquaculture varies depending on where the cages are located, which species are kept, how densely cages are stocked and what the fish are fed.
Important species-specific variables include the species' food conversion ratio FCR and nitrogen retention. A type of salmon called the AquAdvantage salmon has been genetically modified for faster growth, although it has not been approved for commercial use, due to controversy. While some forms of aquaculture can be devastating to ecosystems, such as shrimp farming in mangroves, other forms can be very beneficial.
Shellfish aquaculture adds substantial filter feeding capacity to an environment which can significantly improve water quality. A single oyster can filter 15 gallons of water a day, removing microscopic algal cells. By removing these cells, shellfish are removing nitrogen and other nutrients from the system and either retaining it or releasing it as waste which sinks to the bottom. By harvesting these shellfish the nitrogen they retained is completely removed from the system.
Repackaging these nutrients can relieve eutrophic, or nutrient-rich, conditions known for their low dissolved oxygen which can decimate species diversity and abundance of marine life. Removing algal cells from the water also increase light penetration, allowing plants such as eelgrass to reestablish themselves and further increase oxygen levels. Aquaculture in an area can provide for crucial ecological functions for the inhabitants. Shellfish beds or cages can provide habitat structure. This structure can be used as shelter by invertebrates, small fish or crustaceans to potentially increase their abundance and maintain biodiversity.
Increased shelter raises stocks of prey fish and small crustaceans by increasing recruitment opportunities in turn providing more prey for higher trophic levels.
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One study estimated that 10 square meters of oyster reef could enhance an ecosystem's biomass by 2. This moves energy directly from primary producers to higher trophic levels potentially skipping out on multiple energetically-costly trophic jumps which would increase biomass in the ecosystem. As with the farming of terrestrial animals, social attitudes influence the need for humane practices and regulations in farmed marine animals.
Under the guidelines advised by the Farm Animal Welfare Council good animal welfare means both fitness and a sense of well being in the animal's physical and mental state. This can be defined by the Five Freedoms :.