Användare:Tanzania/Översättningar/6

En räkodling är en akvakulturell odling för marina räkor^[A] för mänsklig konsumtion. Kommersiell räkodling tog sin början under 1970-talet och produktionen ökade lavinartat, framförallt för att leva upp till marknadskraven från USA, Japan och västra Europa. Den totala globala produktionen av odlade räkor nådde mer än 1,6 miljoner ton 2003, till ett världe av närmare 9 miljarder amerikanska dollar. Runt 75% av de odlade räkorna produceras i Asien, framförallt i Kina och Thailand. Återstående 25% produceras huvudsakligen i Latinamerika, där Brasilien är den största producenten. Den största exportnationen är Thailand.

Räkodlingen har ändrats från traditionella småskaliga företag i Sydostasien till en global industri. Teknologiska framsteg har lett till allt tätande odling av räkor, och avelsbeståndet sänds över hela världen. Virtuellt kommer alla odlade räkor från familjen penaeidae och enbart två arter av räkor—Penaeus vannamei och Penaeus monodon—står för drygt 80% av alla odlade räkor. Dessa industriella monokulturer är väldigt mottagliga för sjukdomar vilket på en regional nivå flera gånger har slagit ut stora delar av beståndet av de odlade räkorna. Ökande ekologiska problem, repeterade sjukdomsutbrott och tryck och kritik från både ickestatliga organisationer och konsumentländer ledde till förändringar i industrin under 1990-talets senare del och allmänt hårdare regleringar av regeringar. 1999 initierades ett program som syftade på att förbättra och befrämja mer hållbara jordbruk vilket inkluderade statliga organ, industrirepresentanter och miljöorganisationer.

Räkor har odlats i århundraden i Asien, med hjälp av traditionella lågdensitetsmetoder. Indonesiska bräckvattensdammar kallade tambaks kan spåras tillbaka till 1400-talet. Räkor odlades på liten skala i dammar, i monokulturer eller tillsammans med andra arter såsom mjölkfisk eller i växelbruk med ris där man använde riset som risfält för räkkulturer under torrperioden, när inget ris kunde odlas.^[1] Sådana traditionella kulturer var ofta småföretag i kustområden eller på flodbanker. Mangroveområden favoriserades på grund av deras överflödiga räkbestånd.^[2] Vilda juvenila räkor fångades i dammar och föddes upp på naturligt förekommande organismer i vattnet tills de hade den önskade storleken varpå de skördades.

Industriella räkodlingars ursprung kan spåras tillbaka till 1930-talet när Penaeus japonicus frambringades och odlades för första gången i Japan. Under 1960-talet började en liten räkodlingsindustri utvecklas i Japan.^[3] Kommersiell räkodling började under 1960-talets slut och 1970-talet början. Teknologiska framsteg ledde till än intensivare former av räkodling, och den ökade marknadsefterfrågan ledde till en spridning av räkodlingar över hela världen, koncentrerade i tropiska och subtropiska regioner. Den ökade konsumentefterfrågan sammanföll under 1980-talet med vacklandet av vildräksfångster, vilket skapade ett riktigt uppskjut i räkakvakulturen. Taiwan var bland de första att uppta detta och blev en större producent under 1980-talet. Dess produktion kollapsade med start 1988 på grund av dåligt styre och sjukdomar.^[4] I Thailand ökade den storskaliga intensiva räkodlingen snabbt från 1985.^[5] I Sydamerika banade Ecuador vägen för räkodlingen, där den expanderade kraftigt från 1978.^[6] Brasilien hade blivit aktiv i räkodlingen från 1974, men handeln blev riktigt stor först under 1990-talet vilket gjorde landet till en större producent inom ett fåtal år.^[7] Idag finns det marina räkodlingar i över femtio länder.

När räkodlingen blev ett ekonomiskt genomförbart alternativ för att klara den växande marknadsefterfrågan under 1970-talet som hade blivit större än vad man kunde fånga vilda räkor med, ersattes de gamla subsistensjordbruksmetoderna med mer intensiva sätt med en exportorienterad organisering. Industriella räkodlingar följde först dessa traditionella metoder med så kallade extensiva räkodlingar, men kompenserade för det låga utbytet per område med utökade dammstorlekar. Istället på dammar på bara några få hektar användes dammar uppemot 100 hektar (1 km²) på vissa ställen. Den initialt stora oreglerade marknaden sköt i höjden, och i många regioner ändrades hela kustlinjer och stora mangroveområden rensades. Vidare teknologiska framsteg gjorde mer intensiva odlingsmetoder möjliga som kunde ge högre utbyte per område med mindre använt land. Semi-intensiva och intensiva odlingar kom fram, där räkorna föddes upp på artificiell föda och dammar som bedrevs aktivt. Även om det fortfarande finns många extensiva odlingar är de nya odlingarna vanligtvis intensiva eller semi-intensiva.

Fram till mitten av 1980-talet lagrades de flesta räkodlingarna med unga vildräkor, kallade postlarvae, som vanligtvis fångades av lokala fiskare. Att fiska sådana räkor blev en viktig ekonomisk sektor i många länder. För att motverka den tilltagande uttömningen av fiskemark och för att försäkra en stadig tillgång av unga räkor till odlingar började industrin odla räkor från ägg och behålla vuxna räkor för reproduceringssyften i specialiserade platser som kallas kläckerier.

Räkor mognar och föds upp i marina habitat. Honorna lägger mellan 50 000 och 1 miljon ägg, som kläcks efter ungefär 24 timmar till små larver. Dessa larver äter äggulereserver inuti sina kroppar och undergår därefter en metamorfos till en zoeae. Detta andra larvstadium äter i det vilda alger och undergår efter ett par dagar återigen en metamorfos till det tredje stadiet för att bli myses. Dessa ser redan ut som små räkor och äter alger och djurplankton. Efter ytterligare tre eller fyra dagar genomgår de ytterligare en metamorfos, en sista gång, för att bli en postlarvae, unga räkor som har samma kännetecken som vuxna. Den hela processen tar ungefär 12 dagar från kläckningen. I det vilda flyttar dessa postlarvae till estuarium som är rika på näringsämnen och med en låg salthalt. Där växer det och flyttar senare tillbaka till öppna vatten där de mognar. Vuxna räkor är bentiska och lever huvudsakligen på havsbotten.^[8]

In shrimp farming, this lifecycle occurs under controlled conditions. The reasons to do so include more intensive farming, improved size control resulting in more uniformly sized shrimp, and better predator control, but also the ability to speed up the cycle by controlling the climate (especially in farms in the temperate zones, using greenhouses). There are three different stages:

• Hatcheries breed shrimp and produce nauplii or even postlarvae, which they sell to farms. Large shrimp farms maintain their own hatcheries and sell nauplii or postlarvae to smaller farms in the region.
• Nurseries are those parts of a shrimp farm where postlarvae are grown and accustomed to the marine conditions in the growout ponds.
• In the growout ponds the shrimp are grown from juveniles to marketable size, which takes between three to six months.

Most farms produce one to two harvests a year; in tropical climates, a farm may even produce three. Because of the need for salt water, shrimp farms are located on or near a coast. Inland shrimp farms have also been tried in some regions, but the need to ship salt water and competition for land with agricultural users led to problems. Thailand banned inland shrimp farms in 1999.^[9]

Small-scale hatcheries are very common throughout Southeast Asia. Often run as family businesses and using a low-technology approach, they use small tanks (less than ten tons) and often low animal densities. They are susceptible to disease, but due to their small size, they can typically restart production quickly after disinfection. The survival rate is anywhere between zero and 90%, depending on a wide range of factors, including disease, the weather, and the experience of the operator.

Greenwater hatcheries are medium-sized hatcheries using large tanks with low animal densities. To feed the shrimp larvae, an algal bloom is induced in the tanks. The survival rate is about 40%.

Galveston hatcheries (named after Galveston, Texas, where they were developed) are large-scale, industrial hatcheries using a closed and tightly controlled environment. They breed the shrimp at high densities in large (15 to 30 ton) tanks. Survival rates vary between zero and 80%, but typically achieve 50%.

In hatcheries, the developing shrimp are fed on a diet of algae and later also brine shrimp nauplii, sometimes (especially in industrial hatcheries) augmented by artificial diets. The diet of later stages also includes fresh or freeze-dried animal protein, for example krill. Nutrition and medication (such as antibiotics) fed to the brine shrimp nauplii are passed on to the shrimp that eat them.^[3]

Many farms have nurseries where the postlarval shrimp are grown into juveniles for another three weeks in separate ponds, tanks, or so-called raceways. A raceway is a rectangular, long, shallow tank through which water flows continuously.^[10]

In a typical nursery, there are 150 to 200 animals per square metre. They are fed on a high-protein diet for at most about three weeks before they are moved to the growout ponds. At that time, they weigh between one and two grams. The water salinity is adjusted gradually to that of the growout ponds.

Farmers refer to postlarvae as "PLs", with the number of days suffixed (i.e., PL-1, PL-2, etc.). They are ready to be transferred to the growout ponds after their gills have branched, which occurs around PL-13 to PL-17 (about 25 days after hatching). Nursing is not absolutely necessary, but is favored by many farms because it makes for better food utilization, improves the size uniformity, helps utilize the infrastructure better, and can be done in a controlled environment to increase the harvest. The main disadvantage of nurseries is that some of the postlarval shrimp die upon the transfer to the growout pond.^[3]

Some farms do not use a nursery but stock the postlarvae directly in the growout ponds after having acclimated them to the appropriate temperature and salinity levels in an acclimation tank. Over the course of a few days, the water in these tanks is changed gradually to match that of the growout ponds. The animal density should not exceed 500/liter for young postlarvae and 50/liter for larger ones, such as PL-15.^[11]

In the growout phase, the shrimp are grown to maturity. The postlarvae are transferred to ponds where they are fed until they reach marketable size, which takes about another three to six months. Harvesting the shrimp is done by fishing them from the ponds using nets or by draining the ponds. Pond sizes and the level of technical infrastructure vary.

Extensive shrimp farms using traditional low-density methods are invariably located on a coast and often in mangrove areas. The ponds range from just a few to more than 100 hectares; shrimp are stocked at low densities (2–3 animals per square metre, or 25,000/ha)Mall:Fn. The tides provide for some water exchange, and the shrimp feed on naturally occurring organisms. In some areas, farmers even grow wild shrimp by just opening the gates and impounding wild larvae. Prevalent in poorer or less developed countries where land prices are low, extensive farms produce annual yields from 50 to 500 kg/ha of shrimp (head-on weight). They have low production costs (US$1–3/kg live shrimp), are not very labor intensive, and do not require advanced technical skills.^[12]

Semi-intensive farms do not rely on tides for water exchange but use pumps and a planned pond layout. They can therefore be built above the high tide line. Pond sizes range from 2 to 30 ha; the stocking densities range from 10 to 30/m² (100,000–300,000/ha). At such densities, artificial feeding using industrially prepared shrimp feeds and fertilizing the pond to stimulate the growth of naturally occurring organisms become a necessity. Annual yields range from 500 to 5,000 kg/ha, while production costs are in the range of US$2–6/kg live shrimp. With densities above 15 animals per square metre, aeration is often required to prevent oxygen depletion. Productivity varies depending upon water temperature, thus it is common to have larger sized shrimp in some seasons than in others.

Intensive farms use even smaller ponds (0.1–1.5 ha) and even higher stocking densities. The ponds are actively managed: they are aerated, there is a high water exchange to remove waste products and maintain water quality, and the shrimp are fed on specially designed diets, typically in the form of formulated pellets. Such farms produce annual yields between 5,000 and 20,000 kg/ha; a few super-intensive farms can produce as much as 100,000 kg/ha. They require an advanced technical infrastructure and highly trained professionals for constant monitoring of water quality and other pond conditions; their production costs are in the range of US$4–8/kg live shrimp.

Estimates on the production characteristics of shrimp farms vary. Most studies agree that about 55–60% of all shrimp farms worldwide are extensive farms, another 25–30% are semi-intensive, the rest being intensive farms. Regional variation is high, though, and [Tacon (2002)] reports wide discrepancies in the percentages claimed for individual countries by different studies.^[12]

While extensive farms mainly rely on the natural productivity of the ponds, more intensively managed farms rely on artificial shrimp feeds, either exclusively or as a supplement to the organisms that naturally occur in a pond. A food chain is established in the ponds, based on the growth of phytoplankton. Fertilizers and mineral conditioners are used to boost the growth of the phytoplankton to accelerate the growth of the shrimps. Waste from the artificial food pellets and excrements of the shrimps can lead to the eutrophication of the ponds.

Artificial feeds come in the form of specially formulated, granulated pellets that disintegrate quickly. Up to 70% of such pellets are wasted, as they decay before the shrimps have eaten them.^[3] The shrimps are fed two to five times daily; the feeding can be done manually either from ashore or from boats, or using mechanized feeders distributed all over a pond. The feed conversion rate (FCR), i.e. the amount of food needed to produce a unit (e.g. one kilogram) of shrimp, is claimed by the industry to be around 1.2–2 in modern farms, but this is an optimum value that is not always attained in practice. For a farm to be profitable, a feed conversion rate below 2.5 is necessary; in older farms or under suboptimal pond conditions, the ratio may easily rise to 4:1.^[13] Lower FCRs result in a higher profit for the farm.

Although there are many species of shrimp and prawn, only a few of the larger ones are actually cultivated, all of which belong to the family of penaeids (family Penaeidae),^[14] and within it to the genus PenaeusMall:Fn. Many species are unsuitable for farming: they are too small to be profitable, or simply stop growing when crowded together, or are too susceptible to diseases. The two species dominating the market are:

• Pacific white shrimp (Litopenaeus vannamei, also called "whiteleg shrimp") is the main species cultivated in western countries. Native to the Pacific coast from Mexico to Peru, it grows to a size of 23 cm. P. vannamei accounts for 95% of the production in Latin America. It is easy to breed in captivity, but succumbs to the Taura disease.
• Giant tiger prawn (P. monodon, also known as "black tiger shrimp") occurs in the wild in the Indian Ocean and in the Pacific Ocean from Japan to Australia. The largest of all the cultivated shrimp, it can grow to a length of 36 cm and is farmed in Asia. Because of its susceptibility to whitespot disease and the difficulty of breeding it in captivity, it is gradually being replaced by L. vannamei since 2001.

Together, these two species account for about 80% of the whole farmed shrimp production.^[15] Other species being bred are:

• Western blue shrimp (P. stylirostris) was a popular choice for shrimp farming in the western hemisphere, until the IHHN virus wiped out nearly the whole population in the late 1980s. A few stocks survived and became resistant against this virus. When it was discovered that some of these were also resistant against the Taura virus, some farms again bred P. stylirostris from 1997 on.
• Chinese white shrimp (P. chinensis, also known as the fleshy prawn) occurs along the coast of China and the western coast of Korea and is being farmed in China. It grows to a maximum length of only 18 cm, but tolerates colder water (min. 16 °C). Once a major factor on the world market, it is today used almost exclusively for the Chinese domestic market after a disease wiped out nearly all the stocks in 1993.
• Kuruma shrimp (P. japonicus) is farmed primarily in Japan and Taiwan, but also in Australia; the only market is in Japan, where live Kuruma shrimp reach prices of the order of US$100 per pound ($220/kg).
• Indian white shrimp (P. indicus) is a native of the coasts of the Indian Ocean and is widely bred in India, Iran and the Middle East and along the African shores.
• Banana shrimp (P. merguiensis) is another cultured species from the coastal waters of the Indian Ocean, from Oman to Indonesia and Australia. It can be grown at high densities.

Several other species of Penaeus play only a very minor role in shrimp farming. Some other kinds of shrimp also can be farmed, e.g. the "Akiami paste shrimp" or Metapenaeus spp. Their total production from aquaculture is of the order of only about 25,000 tonnes per year, small in comparison to that of the penaeids.

There are a variety of lethal viral diseases that affect shrimp.^[16] In the densely populated, monocultural farms such virus infections spread rapidly and may wipe out whole shrimp populations. A major transfer vector of many of these viruses is the water itself; and thus any virus outbreak also carries the danger of decimating shrimp living in the wild.

Yellowhead disease, called Hua leung in Thai, affects P. monodon throughout Southeast Asia.^[17] It had been reported first in Thailand in 1990. The disease is highly contagious and leads to mass mortality within 2 to 4 days. The cephalothorax of an infected shrimp turns yellow after a period of unusually high feeding activity ending abruptly, and the then moribund shrimp congregate near the surface of their pond before dying.^[18]

Whitespot syndrome is a disease caused by a family of related viruses. First reported in 1993 from Japanese P. japonicus cultures,^[19] it spread throughout Asia and then to the Americas. It has a wide host range and is highly lethal, leading to mortality rates of 100% within days. Symptoms include white spots on the carapace and a red hepatopancreas. Infected shrimp become lethargic before they die.^[20]

Taura syndrome was first reported from shrimp farms on the Taura river in Ecuador in 1992. The host of the virus causing the disease is P. vannamei, one of the two most commonly farmed shrimp. The disease spread rapidly, mainly through the shipping of infected animals and broodstock. Originally confined to farms in the Americas, it has also been propagated to Asian shrimp farms with the introduction of P. vannamei there. Birds are thought to be a route of infection between farms within one region.^[21]

Infectious Hypodermal and Hematopoietic Necrosis (IHHN) is a disease that causes mass mortality among P. stylirostris (as high as 90%) and severe deformations in P. vannamei. It occurs in Pacific farmed and wild shrimp, but not in wild shrimp on the Atlantic coast of the Americas.^[22]

There are also a number of bacterial infections that are lethal to shrimp. The most common is vibriosis, caused by the bacterium Vibrio spp. The shrimp become weak and disoriented and may have dark wounds on the cuticle. The mortality rate can exceed 70%. Another bacterial disease is Necrotising hepatopancreatitis (NHP); symptoms include a soft exoskeleton and fouling. Most such bacterial infections are strongly correlated to stressful conditions such as overcrowded ponds, high temperatures, and poor water quality: factors that positively influence the growth of bacteria. Treatment is done using antibiotics.^[23] Importing countries have repeatedly placed import bans on shrimp containing various antibiotics. One such antibiotic is chloramphenicol, which has been banned in the European Union since 1994, but continues to pose problems.^[24]

With their high mortality rates, diseases represent a very real danger to shrimp farmers, who may lose their income for the whole year if their ponds are infected. Since most diseases cannot yet be treated effectively, the industry's efforts are focused on preventing diseases to break out in the first place. Active water quality management helps avoid poor pond conditions favourable to the spread of diseases, and instead of using larvae from wild catches, specific pathogen free broodstocks raised in captivity in isolated environments and certified not to carry diseases are used increasingly.^[25] To avoid introducing diseases into such disease-free populations on a farm, there is also a trend to create more controlled environments in the ponds of (semi-)intensive farms, such as by lining them with plastic to avoid soil contact, and by minimizing water exchange in the ponds.^[6]

The total global production of farmed shrimp reached more than 1.6 million tonnes in 2003, representing a farm-gate value of nearly 9 billion U.S. dollars.^[26] This accounts for 25% of the total shrimp production that year (farming and wild catches combined).^[27] The largest single market for shrimp is the United States, importing between 500 – 600,000 tonnes of shrimp products yearly in the years 2003-2009.^[28] About 200,000 tonnes yearly are imported by Japan,^[29][30] while the European Union imported in 2006 another ca. 500,000 tonnes of tropical shrimps, with the largest importers being Spain and France.^[31] The EU also is a major importer or coldwater shrimp from catches, mainly Common shrimp (Crangon crangon) and Pandalidae such as Pandalus borealis; in 2006, these imports accounted for another ca. 200,000 tonnes.^[32]

The import prices for shrimp fluctuate wildly. In 2003 the import price per kilogram shrimp in the United States was US$ 8.80, slightly higher than in Japan at US$8.–. The average import price in the EU was only about US$5.–/kg; this much lower value is explained by the fact that the EU imports more coldwater shrimp (from catches) that are much smaller than the farmed warm water species and thus attain lower prices. In addition, Mediterranean Europe prefers head-on shrimp which weigh approximately 30% more but have a lower unit price.^[33]

About 75% of the world production of farmed shrimp comes from Asian countries; the two leading nations being China and Thailand, closely followed by Vietnam, Indonesia, and India. The other 25% are produced in the western hemisphere, where the South-American countries (Brazil, Ecuador, Mexico) dominate.^[26] In terms of export, Thailand is by far the leading nation with a market share of more than 30%, followed by China, Indonesia, and India, accounting each for about 10%. Other major export nations are Vietnam, Bangladesh, and Ecuador.^[34] Thailand exports nearly all of its production, while China uses most of its shrimp in the domestic market. The only other major export nation that has a strong domestic market for farmed shrimp is Mexico.^[6]

Disease problems have repeatedly impacted the shrimp production negatively. Besides the near-wipeout of P. chinensis in 1993, there were outbreaks of viral diseases that led to marked declines in the per-country production in 1996/97 in Thailand and repeatedly in Ecuador.^[35] In Ecuador alone, production suffered heavily in 1989 (IHHN), 1993 (Taura), and 1999 (whitespot).^[36] Another reason for sometimes wild changes in shrimp farm output are the import regulations of the destination countries, which do not allow shrimp contaminated by chemicals or antibiotics to be imported.

In the 1980s and through much of the 1990s, shrimp farming promised high profits. The investments required for extensive farms were low, especially in regions with low land prices and wages. For many tropical countries, especially those with poorer economies, shrimp farming was an attractive business, offering jobs and incomes for poor coastal populations and has, due to the high market prices of shrimp, provided many developing countries with non-negligible foreign currency earnings. Many shrimp farms were funded initially by the World Bank or substantially subsidized by local governments.^[2]

In the late 1990s, the economic situation changed. Governments and farmers alike were under increasing pressure from NGOs and the consumer countries, who criticized the practices of the trade. International trade conflicts erupted, such as import bans by consumer countries on shrimp containing antibiotics, the United States' shrimp import ban against Thailand in 2004 as a measure against Thai shrimp fishers not using Turtle Excluder Devices in their nets,^[37] or the "anti-dumping" case initiated by U.S. shrimp fishers in 2002 against shrimp farmers worldwide,^[38] which resulted two years later in the U.S. imposing anti-dumping tariffs of the order of about 10% against many producer countries (except China, which received a 112% duty).^[39] Diseases caused significant economic losses. In Ecuador, where shrimp farming was a major export sector (the other two are Bananas and Oil), the whitespot outbreak of 1999 caused an estimated 130,000 workers to lose their jobs.^[6] Furthermore, shrimp prices dropped sharply in 2000.^[40] All of these factors contributed to the slowly growing acceptance by farmers that improved farming practices were needed, and resulted in tighter government regulation of the business, both of which internalized some of the external costs that were ignored during the boom years.^[2][6]

Shrimp farming offers significant employment opportunities, which may help alleviate the poverty of the local coastal populations in many areas, if it is properly managed.^[41] The published literature on that topic shows large discrepancies, and much of the available data is of anecdotal nature.^[42] Estimates of the labor-intensiveness of shrimp farms range from about three times less^[43] to three times more^[44] than when the same area was used for rice paddies, with much regional variation and depending on the type of farms surveyed. In general, intensive shrimp farming requires more labour per unit area than extensive farming. Extensive farms cover much more land area and are often but not always located in areas where no agricultural land uses are possible.^[45] Supporting industries such as feed production or storage, handling, and trade companies should also not be neglected, even if not all of them are exclusive to shrimp farming.

Typically, workers on a shrimp farm can get better wages than with other employments. A global estimate from one study is that a shrimp farm worker can earn 1.5 – 3 times as much as in other jobs;^[46] a study from India arrived at a salary increase of about 1.6,^[44] and a report from Mexico states that the lowest paid job at shrimp farms was paid in 1996 at 1.22 times the average worker salary in the country.^[47]

NGOs have frequently criticized that most of the profits went to large conglomerates instead of to the local population. While this may be true in certain regions such as Ecuador, where most shrimp farms are owned by large companies, it does not apply in all cases. For instance in Thailand, most farms are owned by small local entrepreneurs, although there is a trend to vertically integrate the industries related to shrimp farming from feed producers to food processors and trade companies. A 1994 study reported that a farmer in Thailand could increase his income by a factor of ten by switching from growing rice to farming shrimp.^[48] An Indian study from 2003 arrives at similar figures for shrimp farming in the East Godavari district in Andhra Pradesh.^[49]

Whether the local population benefits from shrimp farming is also dependent on the availability of sufficiently trained people.^[50] Extensive farms tend to offer mainly seasonal jobs during harvest that do not require much training. In Ecuador, many of these positions are known to have been filled by migrant workers.^[51] More intensive farms have a need for year-round labour in more sophisticated jobs.

For commercialization, shrimps are graded and marketed in different categories. From complete shrimps (known as "head-on, shell-on" or HOSO) to peeled and deveined (P&D), any presentation is available in stores. The animals are graded by their size uniformity and then also by their count per weight unit, with larger shrimps attaining higher prices.

Shrimp farms of all types, from extensive to super-intensive, can cause severe ecological problems wherever they are located. For extensive farms, huge areas of mangroves were cleared, reducing biodiversity. During the 1980s and 1990s, about 35% of the world's mangrove forests have vanished. Shrimp farming was a major cause of this, accounting for over a third of it according to one study;^[55] other studies report between 5% and 10% globally, with enormous regional variability. Other causes of mangrove destruction are population pressure, logging, pollution from other industries, or conversion to other uses such as salt pans.^[2] Mangroves, through their roots, help stabilize a coastline and capture sediments; their removal has led to a marked increase of erosion and less protection against floods. Mangrove estuaries are also especially rich and productive ecosystems and provide the spawning grounds for many species of fish, including many commercially important ones.^[4] Many countries have protected their mangroves and forbidden the construction of new shrimp farms in tidal or mangrove areas. The enforcement of the respective laws is often problematic, though, and especially in the least developed countries such as Bangladesh, Myanmar, or Vietnam the conversion of mangroves to shrimp farms remains an issue.^[2]

Intensive farms, while reducing the direct impact on the mangroves, have other problems. Their nutrient-rich effluents (industrial shrimp feeds disintegrate quickly, as little as 30% are actually eaten by the shrimp with a corresponding economic loss to the farmer, the rest is wasted^[3]) are typically discharged into the environment, seriously upsetting the ecological balance. These waste waters contain significant amounts of chemical fertilizers, pesticides, and antibiotics that cause pollution of the environment. Furthermore, releasing antibiotics in such ways injects them into the food chain and increases the risks of bacteria becoming resistant against them.^[56] However, most aquatic bacteria, unlike bacteria associated with terrestrial animals, are not zoonotic. Only a few disease transfers from animals to humans have been reported.^[57]

Prolonged use of a pond can lead to an incremental build-up of a sludge at the pond's bottom from waste products and excrements.^[58] The sludge can be removed mechanically or dried and plowed to allow bio-decomposition, at least in areas without acid problems. Flushing a pond never completely removes this sludge, and eventually, the pond is abandoned, leaving behind a wasteland with the soil made unusable for any other purposes due to the high levels of salinity, acidity, and toxic chemicals. A typical pond in an extensive farm can be used only a few years. An Indian study estimated the time to rehabilitate such lands to about 30 years.^[4] Thailand has banned inland shrimp farms since 1999 because they caused too much destruction of agricultural lands due to salination.^[9] A Thai study estimated that 60% of the shrimp farming area in Thailand was abandoned in the years 1989 – 1996.^[5] Much of these problems stem from using mangrove land that has high natural pyrite content (acid sulfate soil) and poor drainage. The shift to semi-intensive farming requires higher elevations for drain harvesting and low sulfide (pyrite) content to prevent acid formation when the soils shift from anaerobic to aerobic conditions.

The global nature of the shrimp farming business and in particular the shipment of broodstock and hatchery products throughout the world have not only introduced various shrimp species as exotic species, but also distributed the diseases the shrimp may carry worldwide. As a consequence, most broodstock shipment require health certificates and/or to be SPF (specific pathogen free) status. Many organizations lobby actively for consumers to avoid buying farmed shrimp; some also advocate the development of more sustainable farming methods.^[59] A joint programme of the World Bank, the Network of Aquaculture Centres in Asia-Pacific (NACA), the WWF, and the FAO was established in August 1999 to study and propose improved practices for shrimp farming.^[60] Some existing attempts at sustainable export-oriented shrimp farming marketing the shrimp as "ecologically produced" are criticized by NGOs as being dishonest and trivial window-dressing.^[61]

Yet the industry has been slowly changing since about 1999. It has adopted the "best management practices"^[62] developed by e.g. the World Bank et al. programme^[63] and instituted educational programmes to promote them.^[64] Due to the mangrove protection laws enacted in many countries, new farms are usually of the (semi-)intensive kind, which are best constructed outside of mangrove areas anyway. There is a trend to create even more tightly controlled environments in these farms with the hope to achieve better disease prevention.^[6] Waste water treatment has attracted considerable attention; modern shrimp farms routinely have effluent treatment ponds where sediments are allowed to settle at the bottom and other residuals are filtered. As such improvements are costly, the World Bank et al. programme also recommends low-intensity polyculture farming for some areas. Since it has been discovered that mangrove soils are effective in filtering waste waters and tolerate high nitrate levels, the industry has also developed an interest in mangrove reforestation, although its contributions in that area are still minor.^[2] The long-term effects of these recommendations and industry trends cannot be evaluated conclusively yet.

Shrimp farming in many cases has far-reaching effects on the local coastal population. Especially in the boom years of the 1980s and 1990s, when the business was largely unregulated in many countries, the very fast expansion of the industry caused significant changes that sometimes were detrimental to the local population. Conflicts can be traced back to two root causes: competition for common resources such as land and water, and changes induced by wealth redistribution.

A significant problem causing much conflict in some regions, for instance in Bangladesh, are the land use rights. With shrimp farming, a new industry expanded into coastal areas and started to make exclusive use of previously public resources. In some areas, the rapid expansion resulted in the local coastal population being denied access to the coast by a continuous strip of shrimp farms with serious impacts on the local fisheries. Such problems were compounded by poor ecological practices that caused a degradation of common resources (such as excessive use of freshwater to control the salinity of the ponds, causing the water table to sink and leading to the salination of freshwater aquifers by an inflow of salt water).^[65] With growing experience, countries usually introduced stronger governmental regulations and have taken steps to mitigate such problems, for instance through land zoning legislations. Some late adopters have even managed to avoid some problems through proactive legislation, e.g. Mexico.^[6] The situation in Mexico is unique owing to the strongly government-regulated market. Even after the liberalisation in the early 1990s, most shrimp farms are still owned and controlled by locals or local co-ops (ejidos).^[66]

Social tensions have occurred due to changes in the wealth distribution within populations. The effects of this are mixed, though, and the problems are not unique to shrimp farming. Changes in the distribution of wealth tend to induce changes in the power structure within a community. In some cases, there is a widening gap between the general population and local élites who have easier access to credits, subsidies, and permits and thus are more likely to become shrimp farmers and benefit more.^[67] In Bangladesh, on the other hand, local élites were opposing shrimp farming, which was controlled largely by an urban élite.^[68] Land concentrations in a few hands has been recognized to carry an increased risk of social and economic problems developing, especially if the landowners are non-local.^[67]

In general, it has been found that shrimp farming is accepted best and introduced most easily and with the greatest benefits for the local communities if the farms are owned by local people instead of by restricted remote élites or large companies because local owners have a direct interest in maintaining the environment and good relations with their neighbors, and because it avoids the formation of large-scale land property.^[69]

• Freshwater prawn farming shares many characteristics and problems with marine shrimp farming. Unique problems are introduced by the main species' (the giant river prawn, Macrobrachium rosenbergii) developmental life cycle.^[70] The global annual production of freshwater prawns (excluding crayfish and crabs) in 2003 was about 280,000 tonnes, of which China produced some 180,000 tonnes, followed by India and Thailand with some 35,000 tonnes each. China also produced about 370,000 tonnes of Chinese mitten crab (Eriocheir sinensis).^[71]
• Shrimp fishery
• Krill fishery

^A  The terminology is sometimes confusing as the distinction between "shrimp" and "prawn" is often blurred. The FAO, for instance, calls P. monodon the "Giant Tiger Prawn", but P. vannamei the "Whiteleg Shrimp". Recent aquaculture literature increasingly uses the term "prawn" only for the freshwater forms of palaemonids and "shrimp" for the marine penaeids.^[8]

^B  Since adult shrimp are bottom dwellers, stocking densities in ponds are usually given per area, not per water volume.

^C  The taxonomy of the whole genus Penaeus is in flux. Pérez Farfante and Kensley^[72] have proposed a subdivision or reassignment of several species in this genus to new genera based on morphological differences, in particular their genital characteristics. See Penaeus for more information. As a consequence, some of the farmed species are also known under names using the genera Litopenaeus, Farfantepenaeus, Fenneropenaeus, or Marsupenaeus instead of plain Penaeus. Penaeus vannamei, for instance, has become Litopenaeus vannamei.

^D  Accurate statistics on shrimp farming do not exist.^[73] The FAO relies on the voluntary reporting of countries for its fisheries databases; if no numbers are reported, the FAO fills in its own "guesstimate". Such estimates are marked in the databases, but these obviously also contain estimates made already by the reporting government agencies, recognizable only by the suspiciously round numbers.

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