Chapter 12. Aquaculture
Writing team: Patricio Bernal (Group of Experts), Doris Oliva
1. Scale and distribution of aquaculture
Aquaculture is providing an increasing contribution to world food security. At a average annual growth rate of 6.2 per cent between 2000 and 2012 (9.5 per cen between 1990 and 2000), aquaculture is the world’s fastest growing animal foo producing sector (FAO, 2012; FAO 2014). In 2012, farmed food fish contributed  record 66.6 million tons, equivalent to 42.2 per cent of the total 158 million tons o fish produced by capture fisheries and aquaculture combined (including non-foo uses, see Figure 1). Just 13.4 per cent of fish production came from aquaculture i 1990 and 25.7 per cent in 2000 (FAO, 2014).
In Asia, since 2008 farmed fish production has exceeded wild catch (freshwater an marine), reaching 54 per cent of total fish production in 2012; in Europe aquacultur production is 18 per cent of the total and in other continents is less than 15 per cent Nearly half (49 per cent) of all fish consumed globally by people in 2012 came fro aquaculture (FAO, 2014).
Production
7.9 Discard* (Marine capture)
1.9 Aquaculture, inland
24.7 Aquaculture, marine
80 NSS. SSS. 11.6 Capture, inland
Million tonne  co
79.7 Capture, marine
 1950 1960 1970 1980 1990 2000 2010 2012
Figure 1. World capture fisheries and aquaculture production between 1950 and 2012 (HLPE, 2014).
In 2012, world aquaculture production, for all cultivated species combined, was 90. million tons (live weight equivalent and 144.4 billion dollars in value). This include 44.2 million tons of finfish (87.5 billion dollars), 21.6 million tons of shellfis (crustacea and molluscs with 46.7 billion dollars in value) and 23.8 million tons o aquatic algae (mostly seaweeds, 6.4 billion dollars in value). Seaweeds and othe algae are harvested for use as food, in cosmetics and fertilizers, and are processed t extract thickening agents used as additives in the food and animal feed industries Finally 22,400 tons of non-food products are also farmed (with a value of 222. million dollars), such as pearls and seashells for ornamental and decorative use (FAO, 2014).
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According to the latest (but incomplete) information for 2013, FAO estimates tha world food fish aquaculture production rose by 5.8 per cent to 70.5 million tons with production of farmed aquatic plants (including mostly seaweeds) bein estimated at 26.1 million tons.
2. Composition of world aquaculture production: inland aquaculture an mariculture
Although this Chapter is part of an assessment of food security and food safety fro the ocean, to understand the trends in the development of world aquaculture an its impact on food security it is relevant to compare inland aquaculture, conducted i freshwater and saline estuarine waters in inland areas, versus true mariculture conducted in the coastal areas of the world ocean.
Of the 66.6 million tons of farmed food fish’ produced in 2012, two-thirds (44. million tons) were finfish species: 38.6 million tons grown from inland aquacultur and 5.6 million tons from mariculture. Inland aquaculture of finfish now accounts fo 57.9 percent of all farmed food fish production globally.
Although finfish species grown from mariculture represent only 12.6 percent of th total farmed finfish production by volume, their value (23.5 billion United State dollars) represents 26.9 percent of the total value of all farmed finfish species. This i because mariculture includes a large proportion of carnivorous species, such a salmon, trouts and groupers, “cash-crops” higher in unit value and destined to mor affluent markets.
FAO (2014) concludes that freshwater fish farming makes the greatest direc contribution to food security, providing affordable protein food, particularly for poo people in developing countries in Asia, Africa and Latin America. Inland aquacultur also provides an important new source of livelihoods in less developed regions an can be an important contributor to poverty alleviation.
3. Main producers of aquaculture products
In 2013, China produced 43.5 million tons of food fish and 13.5 million tons o aquatic algae (FAO, 2014, p 18), making it by far the largest producer of aquacultur products in the world. Aquaculture production is still concentrated in few countrie of the world. Considering national total production, the top five countries (all in Asia China, India, Viet Nam, Indonesia, Bangladesh) account for 79.8 per cent of worl production while the top five countries in finfish mariculture (Norway, China, Chile Indonesia, and Philippines) account for 72.9 per cent of world production (Table 1 Figure 2).
"The generic term “farmed food fish” used here and by FAO, includes finfishes, crustaceans, molluscs amphibians, freshwater turtles and other aquatic animals (such as sea cucumbers, sea urchins, se squirts and edible jellyfish) produced for intended use as food for human consumption.
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4. Species cultivated
It is estimated that more than 600 aquatic species are cultured worldwide’ in  variety of farming systems and facilities of varying technological sophistication, usin freshwater, brackish water and marine water (FAO, 2014). In 2006, the top 2 species being farmed accounted for over 90 percent of world production (FAO 2006a). Of the more than 200 species of fish and crustaceans currently estimated t be cultivated and fed on externally supplied feeds, just 9 species account for 62. percent of total global-fed species production, including grass car (Ctenopharyngodon idellus), common carp (Cyprinus carpio), Nile tilapi (Oreochromis niloticus), catla (Catla catla), whiteleg shrimp (Litopenaeus vannamei) crucian carp (Carassius carassius), Atlantic salmon (Salmo solar), pangasiid catfishe (striped/tra catfish [Pangasianodon hypophthalmus] and basa catfish [Pangasiu bocourti]), and rohu (Labeo rohita; Tacon et al., 2011). The farming of freshwate tilapias, including Nile tilapia and some other cichlid species, is the most widesprea type of aquaculture in the world. FAO has recorded farmed tilapia productio statistics for 135 countries and territories on all continents (FAO, 2014). In thi respect, aquaculture is no different from animal husbandry, in that global livestoc production is concentrated in a few species (Tacon et al. 2011).2 Among mollusc only 6 species account for the 64.5per cent of the aquaculture production (15. million tons in 2013) and all of them are bivalves: the cupped oyster (Crassostre spp), Japanese carpet shell (Ruditapes philippinarum), constricted Tagelu (Sinnovacula constricta), blood cocked Anadara granosa, Chilean mussel (Mytilu chilensis) and Pacific cupped oyster (Crassostrea gigas).
2 Up to 2012, the number of species registered in FAO statistics was 567, including finfishes (35 species, with 5 hybrids), molluscs (102), crustaceans (59), amphibians and reptiles (6), aquati invertebrates (9), and marine and freshwater algae (37).
3 on land, the top eight livestock species are pig, chicken, cattle, sheep, turkey, goat, duck and buffal (Tacon et al. 2011)
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Table 1. Farmed food fish production by 15 top producers and main groups of farmed species in 201 (FAO, 2014).
Finfish Crustaceans Molluscs Other Daa teTar 1 Pre ma Producer oa Ce ee Pyrat Beas) Deletes |]
[ecte China 23341134 1028399 3592588 12343169 803016 41 108 306 61. India 3812420 84164 299926 12.905 wa. 4209.415 6 Viet Nam 2091200 51000 513100 400000 30200 3085500 4 Indonesia 2097407 582077 387698 ae 477-3067 660 4 Bangladesh 1525672 63220 137174 oe 1726 066 2 Norway 85 1319033 7 2001 ve 1321119 2. Thailand 380986 19994 623660 205192 4045 «1233877 1 Chile 59527 758 587 we 253 307 w.-1077 421 1. Egypt 1016 629 oe 1109 oe w.-1017 738 1 Myanmar 822589 1868 58981 a. «1731 885 169 1 Philippines 310042 361722. —- 72822 46 308 7 790 894 1 Brazil 611343 TA ANS 20699 1005 707 461  Japan 33957 250 472 1596 3459141108 633 047 1. Republic of 14099 76 307 2838 373488 17672 484.404 0. United States 185598 21169 44.928 168 329 ce 420 024 0.6
Top 15 subtotal 36302688 4618012 5810835 14171312 859254 61762101 92.7
Rest of world 2296562 933893 635 983 999 426 5 288 4871 152 7. World 38599250 5551905 6446818 15170738 864542 66633253 100
Note: The symbol “..." means the production data are not available or the production volume is regarded a negligibly low.
5. Aquaculture systems development
The cultivation of farmed food fish is the aquatic version of animal husbandry, wher full control of the life cycle enables the domestication of wild species, their growth i large-scale farming systems and the application of well-known and well-establishe techniques of animal artificial selection of desirable traits, such as resistance t diseases, fast growth and size.
For most farmed aquatic species, hatchery and nursery technologies have bee developed and well established, enabling the artificial control of the life cycle of th species. However wild seed is still used in many farming operations. For a fe species, such as eels (Anguilla spp.), farming still relies entirely on wild seed (FAO 2014).
Aquaculture can be based on traditional, low technology farming systems or o highly industrialized, capital-intensive processes. In between there is a whole rang of aquaculture systems with different efficiencies that can be adapted to loca socioeconomic contexts.
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Physically, inland aquaculture and coastal shrimp mariculture uses fixed ponds an raceways on land that put a premium on the use of land. Finfish mariculture an some farming of molluscs such as oysters and mussels tend to use floating net pens cages and other suspended systems in the water column of shallow coastal waters enabling these systems to be fixed by being anchored to the bottom.
Direct land use needs for fish and shrimp ponds can be substantial. Curren aquaculture production occupies a significant quantity of land, both in inland an coastal areas. Aquaculture land use efficiency, however, differs widely by productio system. While fish ponds use relatively high amounts of land (Costa-Pierce et al. 2012, cited in WRI, 2014), flow-through systems (raceways) use less land, whil cages and pens suspended in water bodies use very little (if any) land (WRI, 2014).
The handling of monocultures with high densities of individuals in confinemen replicates the risks typical to monocultures in land-based animal husbandry, such a the spread and proliferation of parasites, and the contagion of bacterial and vira infections producing mass mortalities, and the accumulation of waste products. If o land these risks can be partially contained, in mariculture, the use of semi-enclose systems open to the natural flow of seawater and sedimentation to the bottom propagate these risks to the surrounding environment affecting the health of th ecosystems in which aquaculture operations are implanted.
The introduction of these risks to the coastal zones puts a premium in th application of good management practices and effective regulations for zoning, sit selection and maximum loads per area.
In 1999 during the early development of shrimp culture, a White Spot Syndrom Virus (WSSV) epizootic quickly spread through nine Pacific coast countries in Lati America, costing billions of dollars (McClennen, 2004). Disease outbreaks in recen years have affected Chile’s Atlantic salmon production with losses of almost 5 percent to the virus of “infectious salmon anaemia” (ISA). Oyster cultures in Europ were attacked by herpes virus Os HV-1 or OsHV-1 wvar, and marine shrimp farmin in several countries in Asia, South America and Africa have experienced bacterial an viral infections, resulting in partial or sometimes total loss of production. In 2010 aquaculture in China suffered production losses of 1.7 million tons caused by natura disasters, diseases and pollution. Disease outbreaks virtually wiped out marin shrimp farming production in Mozambique in 2011 (FAO, 2010, 2012).
New diseases also appear. The early mortality syndrome (EMS) is an emergin disease of cultured shrimp caused by a strain of Vibrio parahaemolyticus, a marin micro-organism native in estuarine waters worldwide. Three species of culture shrimp are affected (Penaeus monodon, P. vannamei and P. chinensis). In Viet Nam about 39 000 hectares were affected in 2011. Malaysia estimated production losse of 0.1 billion dollars (2011). In Thailand, reports indicated annual output declines o 30-70 percent. The disease has been reported in China, Malaysia, Mexico, Thailan and Viet Nam (FAO, 2014).
It is apparent that intensive aquaculture systems are likely to create conditions tha expose them to disease outbreaks. When semi-enclosed systems are used, as i mariculture, pathogens in their resting or reproductive stages propagate directly to
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the environment, where they can persist for long periods of time as a potentia source of recurring outbreaks.
Optimization of industrial systems selects for few or a single preferred species. Thi is the case in the oyster culture with the widespread culture of Crassostrea gigas an in the shrimp industry by the dominance of Penaeus vanamei, the white shrimp a the preferred species. This can be also an additional source of risk, if evolvin pathogens develop resistance to antibiotics or other treatments used to control well known diseases.
6. Fed and non-fed aquaculture
Animal aquaculture production can be divided among those species that feed fro natural sources in the environment in which they are grown, and species that ar artificially fed. The output of naturally-fed aquaculture represents a net increase o world animal protein stock, while the contribution of fed aquaculture, consumin plant or animal protein and fat, depends on conversion rates controlled by th physiology of the species and the effectiveness of the farming system.
In 2012, global production of non-fed species from aquaculture was 20.5 millio tons, including 7.1 million tons of filter-feeding carps and 13.4 million tons o bivalves and other species. Accordingly, 46.09 million tons or 69.2 per cent of tota farmed food fish (FAO, 2014) was dependent upon the supply of external nutrien inputs provided in the form of (i) fresh feed items, (ii) farm-made feeds or (iii commercially manufactured feeds (Tacon et al., 2011).
The share of non-fed species in total farmed food fish production continued t decrease to 30.8 percent in 2012 compared with about 50 percent in 1982, reflectin stronger growth in the farming of fed species, especially of high value carnivore (FAO, 2014).
Million tonne 3 ——— Non-fed: silver & bighead car 30 Non-fed: bivalves  ----- Fed: freshwater finfish ueer seers Fed: diadromous & marine finfish wer 25 Fed: crustaceans _oeo — Fed: molluscs ueor 20 < 15 —= a 10 =  5 as a  00 01 02 03 04 05 06 07 08 09 10 11 1 Figure 2. World aquaculture production, fed and non-fed between years 2000 and 2012 (FAO, 2014)
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In Europe, after much publicly and privately sponsored research, the technology t farm cod was fully developed and supported by large amounts of venture capital and industrial production of cod started. In the early 2000s this industria development suffered from the financial crisis of 2008, and further growth an development almost stopped. Although the participation of risk capital in th development of aquaculture might be an option in particular places an circumstances, it is far from being the preferred option. Development of aquacultur systems, supplying domestic and international markets, has a better chance t succeed if supported by a mix of long-term public support systems (credit, technica assistance) for small and rural producers coupled with entrepreneurial initiative well implanted in the markets.
Marine finfish aquaculture is rapidly growing in the Asia-Pacific region, where high value carnivorous fish species (e.g. groupers, barramundi, snappers and pompano are typically raised in small cages in inshore environments. In China thi development has led to experiments in offshore mariculture using larger an stronger cages. (FAO, 2014).
These examples show that at least to the present, decision-making for th development of mariculture, particularly finfish mariculture, tends to be dominate by economic growth and not by food security considerations. To balance this trend the intergovernmental High Level Panel of Experts on Food Security has recentl advocated the need to define specific policies to support current targets on foo security in view of the projected growth of human population (HLPE, 2014).
The potential for non-fed mariculture development is far from being fully explore particularly that of marine bivalves in Africa and in Latin America and in th Caribbean. Limited capacity in mollusc seed production is regarded as a constraint i some countries (FAO, 2014).
7. Aquafeed production
Total industrial compound aquafeed production increased, from 7.6 million tons i 1995 to 29.2 million tons in 2008 (last estimate available, Tacon et al., 2011). Thes are estimates because there is no comprehensive information on the globa production of farm-made aquafeeds (estimated by FAO at between 18.7 and 30. million tons in 2006) and/or on the use of low-value fish/trash fish as fresh feed.
Fishmeal is used as high-protein feed and fish oil as a feed additive in aquacultur (FAO, 2014). Fishmeal and fish oil are produced mainly from harvesting stocks o small, fastreproducing fish (e.g., anchovies, small sardines and menhaden) and fo which there is some, but limited, demand for human consumption. This use promoted in the 1950s by FAO as a means to add value to the massive harvesting o small pelagic fish, raises the question of the alternative use of this significant fis biomass for direct human consumption (HLPE 2014).
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In 2012 about 35 per cent of world fishmeal production was obtained from fisherie by-products (frames, off-cuts and offal) from the industrial processing of both wil caught and farmed fish. Commercial operations harvesting myctophids’ for fishmea and oil are being piloted in some regions, though the ecological consequences o exploiting these previously untapped resources have not been evaluated. In 200 the largest producer of fishmeal was Peru (1.4 million tons) followed by China (1. million tons) and Chile (0.7 million tons). Other important producers were Thailand the United States of America, Japan, Denmark, Norway and Iceland (Tacon et al. 2011).
Estimates of total usage of terrestrial animal by-product meals and oils in compoun aquafeeds ranges between 0.15 and 0.30 million tons, or less than 1 percent of tota global production.
Patterns in the use of fishmeal and fish oil have changed in time due to the growt and evolution of the world aquaculture industry. On a global basis, in 2008 (the mos recent published estimate), the aquaculture sector consumed 60.8 percent of globa fishmeal production (3.72 million tons) and 73.8 percent of global fish oil productio (0.78 million ons, Tacon et al., 2011). In contrast, the poultry and pork industrie each used nearly 26 per cent and 22 per cent respectively of the available fishmeal i 2002 while aquaculture consumed only 46 percent of the global fishmeal supply an 81 percent of the global fish oil supply (Pike, 2005; Tacon et al., 2006)
Fish oil has become also a product for direct human consumption for health reasons Long-chain Omega-3 fatty acids, specifically EPA and DHA, have been shown to pla a critical role in human health: EPA in the health of the cardiovascular system an DHA in the proper functioning of the nervous system, most notably brain function. I 2010 fish oil for direct human consumption was estimated at 24 per cent of the tota world production, compared with 5 per cent in 1990. (Shepherd and Jackson, 2012).
The total use of fishmeal by the aquaculture sector is expected to decrease in th long term in favour of plant-based materials (Figure 3). It has gone down from 4.2 million tons in 2005 to 3.72 million tons in 2008 (or 12.8 percent of total aquafeed by weight), and is expected to decrease to 3.49 million tons by 2020 (at an estimate 4.9 per cent of total aquafeeds by weight) (Tacon et al., 2011).
These trends reflect that fishmeal is being used by industry as a strategic ingredien fed in stages of the growth cycle where its unique nutritional properties can give th best results or in places where price is less critical (Jackson, 2012). The mos commonly used alternative to fishmeal is that of soymeal. Time series of the price o both products show that use of fishmeal is being reduced in less critical areas such a grower feeds, but remains in the more critical and less price-sensitive areas o hatchery and brood-stock feeds. (Jackson and Shepherd, 2012)
4 Myctophids are small-size mesopelagic fish inhabiting between 200 and 1000 metres tha vertically migrate on a daily basis. Biomass of myctophids is estimated to be considerabl worldwide.
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2010 Total Production
(Million tons = Salmon 2 = Shrimp 4 * Catfish 3. "Tilapia 3 ™Carps (fed) 17.6
1995 2000 2005 2010 2015 202 Note: Fishmeal use varies within and between countries; the figures presented are global means. Data represent observations between 1995-2008, and projections fo 2009-2020.
Source: Tacon and Metian (2008), Tacon et al. (2011).
Figure 3. The aquaculture industry has reduced the share of fishmeal in farmed fish diets (percent (FAO, 2014).
The use of fish oil by the aquaculture sector will probably increase in the long ru albeit slowly. It is estimated that total usage will increase by more than 16 percent from 782,000 tons (2.7 percent of total feeds by weight) in 2008 to the estimate 908.000 tons (1.3 percent of total feeds for that year) by 2020. It is forecast tha increased usage will shift from salmonids, to marine finfishes and crustacean because of the current absence of cost-effective alternative lipid sources that ar rich in long-chain polyunsaturated fatty acids. (Tacon et al., 2011)
8. Economic and social significance
At the global level, the number of people engaged in fish farming has, since 1990 increased at higher annual rates than that of those engaged in capture fisheries. Th most recent estimates (FAO 2014, Table 2) indicate that about 18.9 million peopl were engaged in fish farming, 96 per cent concentrated primarily in Asia, followed b Africa (1.57 percent), Latin America and the Caribbean (1.42 percent), Europe (0.5 per cent), North America (0.04 per cent) and Oceania (0.03 per cent). The 18,17 million fish farmers in 2012 represented 1.45 per cent percent of the 1.3 billio people economically active in the broad agriculture sector worldwide. (FAO, 2014).
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Table 2. FAO (2014) estimates that the total number of fish farmers in the world has grown from  million in 1995 to close to 19 million today, representing an increasing source of livelihoods. Not al these jobs are permanent and year-around, since many are seasonal.
Bh) eielss) ede PLT) 2011 Pia e (eae en
Of which, fish farmer Africa 65 91 140 231 257 29 Asia 7 762 12211 14630 17915 18 373 1817 Europe 56 103 91 102 103 10 Latin America and the 155 214 239 248 265 26 Caribbea North America 6 6 10 9 9  Oceania 4 5 5 5 6 6
World 8049 12 632 15115 18 512 19015 18 861
Out of the 18.8 million of fish farmers in the world (Table 2), China alone employ 5.2 million, representing 27.6 per cent of the total, while Indonesia employs 3. million farmers, representing 17.7 per cent of the total. Employment at farm leve includes full-time, part-time and occasional jobs in hatcheries, nurseries, grow-ou production facilities, and labourers. Employment at other stages along aquacultur value-chains includes jobs in input supply, middle trade and domestic fis distribution, processing, exporting and vending (HLPE, 2014). More than 80 percen of global aquaculture production may be contributed by small- to medium-scale fis farmers, nearly 90 per cent of whom live in Asia (HLPE, 2014). Farmed fish ar expected to contribute to improved nutritional status of households directly throug self-consumption, and indirectly by selling farmed fish for cash to enhanc household purchasing power (HLPE, 2014)
The regional distribution of jobs in the aquaculture sector reflects widely disparat levels of productivity strongly linked to the degree of industrialization of th dominant culture systems in each region. In Asia, low technology is used in non-fe and inland-fed aquaculture, using extensive ponds, which is labour intensiv compared with mariculture in floating systems. In 2011, the annual averag production of fish farmers in Norway was 195 tons per person, compared with 5 tons in Chile, 25 tons in Turkey, 10 tons in Malaysia, about 7 tons in China, about  tons in Thailand, and only about 1 ton in India and Indonesia (FAO, 2014).
Extrapolating from a ten-country case study representing just under 20 percent o the global aquaculture production, Phillips and Subasinghe (2014, persona communication, cited in HLPE, 2014) estimated that “total employment in globa aquaculture value chains could be close to 38 million full-time people.”
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Table 3. Per capita average outputs per fish farmer by region (in FAO, 2014).
Ledeere [Flas tolpke aloe telat
ied 2010 Pith hy
ere ato)
Aquaculture
Africa 44 4.6 5.6 5.4 5. Asia 2.3 2.7 2.9 3.0 3. Europe 19.8 23.5 24.9 26.0 27. Latin America and the Caribbean 3.9 6.3 78 9.0 9. North America 91.5 68.2 70.0 59.5 59. Oceania 23.1 29.5 33.8 30.4 32. World 2.6 2.9 3.2 3.3 3.5
' Production excludes aquatic plants.
Fish is among the most traded food commodities worldwide. Fish can be produced i one country, processed in a second and consumed in a third. There were 129 billio dollars of exports of fish and fishery products in 2012 (FAO, 2014)
In the last two decades, in line with the impressive growth in aquacultur production, there has been a substantial increase in trade of many aquacultur products based on both low- and high-value species, with new markets opening u in developed and developing countries as well as economies in transition.
Aquaculture is contributing to a growing share of international trade in fisher commodities, with high-value species such as salmon, seabass, seabream, shrim and prawns, bivalves and other molluscs, but also relatively low-value species suc as tilapia, catfish (including Pangasius) and carps (FAO 2014). Pangasius is  freshwater fish native to the Mekong Delta in Viet Nam, new to international trade However, with production of about 1.3 million tons, mainly in Viet Nam and all goin to international markets, this species is an important source of low-priced trade fish. The European Union and the United States of America are the main importer of Pangasius. (FAO, 2014)
9. Environmental impacts of aquaculture
Environmental effects from aquaculture include land use and special natural habitat destruction, pollution of water and sediments from wastes, the introduction of non native, competitive species to the natural environment through escapes from farms genetic effects on wild populations (of fish and shellfish) from escapes of farme animals or their gametes, and concerns about the use of wild forage fish fo aquaculture feeds.
9.1 Land use
WRI (2014) estimate that inland aquaculture ponds occupied between 12.7 millio ha and 14.0 million ha of land in 2010, and that brackish water or coastal ponds
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occupied approximately 4.4 million ha—for a combined area of roughly 18 millio hectares, overwhelmingly in Asia. Many of these ponds were converted from ric paddies and other existing cropland rather than newly converted natural lands—bu even so, aquaculture adds to world land use demands.
In 2008, global land use efficiencies of inland and brackish water ponds averaged 2. tons of fish per hectare per year (t/ha/yr). Expanding aquaculture to 140 million ton by 2050 without increases in that average efficiency would imply an additional are of roughly 24 million ha directly for ponds—about the size of the United Kingdom (WRI, 2014)
9.2 Interaction with mangroves
Land conversion for aquaculture can lead to severe ecosystem degradation, as in th case of the proliferation of extensive low-yield shrimp farms that destroyed larg extensions of mangrove forests in Asia and Latin America (Lewis et al., 2002, cited i WRI, 2014). Since the 1990s, non-governmental organizations and policy-maker have focused on curbing the expansion of extensive, shrimp farms into mangrov forests in Asia and Latin America (FAO et al., 2006b) As a result, mangrove clearanc for shrimp farms has greatly decreased, thanks to mangrove protection policies i affected countries and the siting of new, more high-yield shrimp farms away fro mangrove areas. (Lewis et al., 2002).
9.3 Pollution of water and sediments
Wastes from mariculture generally include dissolved (inorganic) nutrients particulate (organic) wastes (feces, uneaten food and animal carcasses), an chemicals for maintaining infrastructure (anti-biofouling agents) and animal healt products (antiparasitics, disinfectants and antibiotics). These wastes impose a additional oxygen demand on the environment, usually creating anoxic condition under pens and cages.
Research in Norway has shown that benthic effects decline rapidly with increasin depth of water under salmon nets, but situating farms as close to shore as possibl may be a prerequisite for economic viability of the industry. Fallowing periods o several years have been found necessary in Norway to allow benthic recovery Research elsewhere indicates that benthic recovery may be quicker under som conditions (WHOI, 2007)
9.4 Impact of escapes
With the use of floating semi-enclosed systems, escapes are inevitable in maricultur and inland aquaculture. Catastrophic events (e.g., hurricanes or other storms) human error, seal and sea lion predation and vandalism will remain potential path for farmed fish to escape into the wild. Advancements in technology are likely t continue to reduce the frequency and severity of escape events but it is unlikely tha this ecological and economic threat will ever disappear entirely. There i considerable evidence of damage to the genetic integrity of wild fish population when escaped farmed fish can interbreed with local stocks. Furthermore, in semi enclosed systems, cultured organisms release viable gametes into the water.
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Mariculture industry has undertaken a significant effort to produce and use variant of cultivated species that are infertile, diminishing the risk of gene-flow fro cultivated/domesticated species to their wild counterparts when escapes occur.
9.5 Non-native species.
Aquaculture has been a significant source of intentional and unintentiona introductions of non-native species into local ecosystems worldwide. The har caused by invasive species is well documented.
Intensive fish culture, particularly of non-native species, can be and has bee involved in the introduction and/or amplification of pathogens and disease in wil populations (Blazer and LaPatra, 2002, cited in WHOI, 2007).
Non-native oysters have been introduced in many regions to improve failing harvest of native varieties due to diseases or overexploitation. The eastern oyster Crassostrea virginica, was introduced to the West Coast of the United States in 1875 The Pacific or Japanese oyster Crassostrea gigas, native to the Pacific coast of Asia has been introduced in North and South America, Africa, Australia, Europe, and Ne Zealand and has also spread through accidental introductions either through larva in ballast water or on the hulls of ships (Helm, 2006).
9.6 Genetically modified organisms
Although the use of transgenic, or genetically modified organisms (GMOs), is no common practice in aquaculture (WHOI, 2007), nevertheless the potential use o GMOs would pose severe risks. The production and commercialization of aquati GMOs should be analyzed considering economic issues, environmental protection food safety and social and health well-being (Muir, et al., 1999; Le Curieux-Belfon et al., 2009).
9.7 Use of chemicals as pesticides and for antifouling
A wide variety of chemicals are currently used in aquaculture production. As th industry expands, it requires the use of more drugs, disinfectants and antifoulin compounds (biocides)° to eliminate the microorganisms in the aquaculture facilities Among the most common disinfectants are hydrogen peroxide and malachite green Pyrethroid insecticides and avermectins are used as anthelmintic agents (Romero e al., 2012). Organic booster biocides were recently introduced as alternatives to th organotin compounds found in antifouling products after restrictions were impose on the use of tributyltin (TBT). The replacement products are generally based o copper metal oxides and organic biocides. The biocides that are most commonl used in antifouling paints include chlorothalonil, dichlofluanid, DCOIT (4,5-dichloro 2-n-octyl-4-isothiazolin-3-one, Sea-nine 211°), Diuron, Irgarol 1051, TCMS pyridine
 Biocides are chemical substances that can deter or kill the microorganisms responsible for biofouling.
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(2,3,3,6-tetrachloro-4-methylsulfonyl pyridine), zinc pyrithione and Zineb. (Guardiol et al., 2012). The use of biocides is not as well-regulated as drug use in aquacultur because the information available on their effects on ecosystems is still limited.
9.8 Use of antibiotics
Antibiotic drugs used in aquaculture may have substantial environmental effects The use of antibiotics in aquaculture can be categorized as therapeutic, prophylacti or metaphylactic. Therapeutic use is the treatment of established infections Metaphylaxis are group-medication procedures, aimed at treating sick animals whil also medicating others in the group to prevent disease. Prophylaxis means th precautionary use of antimicrobials in either individuals or groups to prevent th development of infections (Romero et al., 2012).
In aquaculture, antibiotics at therapeutic levels are frequently administered for shor periods of time via the oral route to groups of fish that share tanks or cages. Fish d not effectively metabolize antibiotics and will pass them largely unused back into th environment in feces. 70 to 80 per cent of the antibiotics administered to fish a medicated pelleted feed are released into the aquatic environment via urinary an fecal excretion and/or as unused medicated food (Romero et al., 2012). For thi among other reasons, antibiotic use in net, pen or cage mariculture is a concer because it can contribute to the development of resistant strains of bacteria in th wild. The spread of antimicrobial resistance due to exposure to antimicrobial agent is well documented in both human and veterinary medicine. It is also wel documented that fish pathogens and other aquatic bacteria can develop resistanc as a result of antimicrobial exposure. Examples include Aeromonas salmonicida Aeromonas hydrophila, Edwardsiella tarda, Yersinia ruckeri, Photobacteriu damselae and Vibrio anguillarum. Research has shown that antibiotics excreted ten to degrade faster in sea-water, while they persist more in sediments. (Romero et al. 2012)
The public health hazards related to antimicrobial use in aquaculture are twofold the development and spread of antimicrobial-resistant bacteria and resistance gene and the presence of antimicrobial residues in aquaculture products and th environment (Romero et al., 2012). The high proportions of antibiotic-resistan bacteria that persist in sediments and farm environments may provide a threat t fish farms because they can act as sources of antibiotic-resistance genes for fis pathogens in the vicinity of the farms. Because resistant bacteria may transfer thei resistance elements to bacterial pathogens, the implementation of efficien strategies to contain and manage resistance-gene emergence and spread is critica for the development of sustainable aquaculture practices.
Industry faced with uncertainties created by the limited knowledge of infectiou diseases and their prevalence in a particular environment tends to abuse the use o antibiotics. Defoirdt et al. (2011, cited by Romero et al., 2012) estimated tha approximately 500-600 metric tons of antibiotics were used in shrimp far production in Thailand in 1994; he also emphasized the large variation betwee different countries, with antibiotic use ranging from 1 g per metric ton of productio in Norway to 700 g per metric ton in Viet Nam. In the aftermath of the ISA infectio in the salmon culture in Chile, SERNAPESCA, the Chilean National Fisheries and
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Aquaculture Service, recently released data reporting unprecedentedly hig amounts of antibiotics used by the salmon industry.° Inefficiencies in the antibioti treatment of fish illnesses now may lead to significant economic losses in the futur (Romero et al., 2012).
Antimicrobial-resistant bacteria in aquaculture also present a risk to public health The appearance of acquired resistance in fish pathogens and other aquatic bacteri means that such resistant bacteria can act as a reservoir of resistance genes fro which genes can be further disseminated and may ultimately end up in huma pathogens. Plasmid-borne resistance genes have been transferred by conjugatio from the fish pathogen A. salmonicida to Escherichia coli, a bacterium of huma origin, some strains of which are pathogenic for humans (Romero et al., 2012).
9.9 Diseases and parasites
Farming marine organisms in dense populations results in outbreaks of viral bacterial, fungi and parasite diseases. Diseases and parasites constitute a stron constraint on the culture of aquatic species and disease and parasite translocatio by host movements in different spatial scales is common. In molluscs the mai parasites are protozoans of the genus Bonamia, Perkinsus and Marteilia. Th pathogens Haplosporidium, bacteria (rickettsial and vibriosis) and herpes-type viru have a great impact on the rates of mortality. In shrimps the most relevant disease are viral (white spot disease, WPS, yellow head disease, YHD, taura syndrom disease, TSD) (Bondad-Reantaso et al., 2005).
The “Sea lice (Copepoda, Caligidae) have been the most widespread pathogeni marine parasite” in Salmon farming, affecting also other cultured fishes and wil species (Ernst et al., 2001; Costello, 2006). The global economic cost of sea lic control was estimated at over 480 million dollars in 2006 (Costello, 2009); however there are other impacts such as the decrease in conversion efficiency (Sinnott, 1998 and the depression of immune systems, which allow the outbreak of bacteria (vibriosis and furuncolosis) and viral diseases (infectious salmon anaemia virus, ISA infectious pancreatic necrosis, IPN and pancreas disease, PD) (Robertson, 2011).
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6 According to SERNAPESCA, the industry used an estimated 450,700 kilos of antibiotics in 2013.
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