Overblog Suivre ce blog
Editer l'article Administration Créer mon blog
17 octobre 2013 4 17 /10 /octobre /2013 04:57

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 elites who have easier access to credits, subsidies, and permits and thus are more likely to become shrimp farmers and benefit more.[81] Toshiba Satellite A100-849 CPU Fan

In Bangladesh, on the other hand, local elites were opposing shrimp farming, which was controlled largely by an urban elite.[82]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.[81] Gateway MT6400 CPU Fan

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. Toshiba Satellite A100-849 CPU Fan

Although shrimp farming has disrupted social structures, it is possible for both commercial industries and independent farmers to succeed. Closed system shrimp aquaculture for instance, is becoming widely used in the US and is making its way to Southeast Asia. This system takes place indoors in moderate sized pools which efficiently circulates the water. Dell Vostro 3350 CPU Fan

In some cases filter feeders such as shellfish and other fish are introduced in the system, feeding off nutrients in the water that would otherwise be cycled out. This option is more environmentally safe than large scale intensive farming practices. Unfortunately, this system is capital intensive and would be difficult for small scale, independent shrimp farmers to acquire. ACER Aspire 4733 CPU Fan

However, this would be an excellent alternative for larger shrimp industries in Thailand.

Another alternative would be to revert to traditional shrimp farming practices, without overstocking and the use of harmful chemicals. ACER Aspire 3003LCi CPU Fan

A freshwater prawn farming is an aquaculture business designed to raise and produce freshwater prawns or shrimp1 for human consumption. Freshwater prawn farming shares many characteristics with, and many of the same problems as, marine shrimp farming. Unique problems are introduced by the developmental life cycle of the main species (the giant river prawn,Macrobrachium rosenbergii).[1] HP Pavilion dv7-6187cl CPU Fan

The global annual production of freshwater prawns (excluding crayfish and crabs) in 2003 was about 280,000 tons, of whichChina produced some 180,000 tons, followed by India and Thailand with some 35,000 tons each. Additionally, China produced about 370,000 tons of Chinese river crab (Eriocheir sinensis). HP Pavilion dv7-1128ca CPU Fan

All farmed freshwater prawns today belong to the genus Macrobrachium. Until 2000, the only species farmed was the giant river prawn (Macrobrachium rosenbergii, also known as the Malaysian prawn). Since then, China has begun farming the Oriental river prawn (M. nipponense) in large quantities, and India farms a small amount of monsoon river prawn (M. malcolmsonii). HP Pavilion dv6-3216us CPU Fan

In 2003, these three species accounted for all farmed freshwater prawns, about two-thirds M. rosenbergii and one-third M. nipponense.

About 200 species in the genus Macrobrachium live in the tropical and subtropical climates on all continents except Europe and Antarctica. HP Pavilion dv6565el CPU Fan\

Giant river prawns live in turbid freshwater, but their larval stages require brackish water to survive. Males can reach a body size of 32 cm; females grow to 25 cm. In mating, the male deposits spermatophores on the underside of the female's thorax, between the walking legs. The female then extrudes eggs, which pass through the spermatophores. DELL Latitude E6410 CPU Fan

The female carries the fertilized eggs with her until they hatch; the time may vary, but is generally less than three weeks. A large female may lay up to 100,000 eggs.

From these eggs hatch zoeae, the first larval stage of crustaceans. They go through several larval stages before metamorphosing into postlarvae, HP Pavilion dv6-2066dx CPU Fan

at which stage they are about 8 mm long and have all the characteristics of adults. This metamorphosis usually takes place about 32 to 35 days after hatching. These postlarvae then migrate back into freshwater.

There are three different morphotypes of males. The first stage is called "small male" (SM); HP 610777-001 CPU Fan

this smallest stage has short, nearly translucent claws. If conditions allow, small males grow and metamorphose into "orange claw" (OC) males, which have large orange claws on their second chelipeds, which may have a length of 0.8 to 1.4 times their body size. OC males later may transform into the third and final stage, the "blue claw" (BC) males. Samsung MCF-913PAM05-40 CPU Fan

These have blue claws, and their second chelipeds may become twice as long as their body.[3]

Male M. rosenbergii prawns have a strict hierarchy: the territorial BC males dominate the OCs, which in turn dominate the SMs. The presence of BC males inhibits the growth of SMs and delays the metamorphosis of OCs into BCs; HP Pavilion dv7-2140eo CPU Fan

an OC will keep growing until it is larger than the largest BC male in its neighbourhood before transforming. All three male stages are sexually active, though, and females which have undergone their premating molt will cooperate with any male to reproduce. BC males protect the females until their shells have hardened; OCs and SMs show no such behavior. HP Envy 15-1060ea CPU Fan

Giant river prawns have been farmed using traditional methods in Southeast Asia for a long time. First experiments with artificial breeding cultures of M. rosenbergii were done in the early 1960s in Malaysia, where it was discovered that the larvae needed brackish water for survival. Industrial-scale rearing processes were perfected in the early 1970s in Hawaii, and spread first to Taiwan and Thailand, and then to other countries. HP Pavilion dv4-2140us CPU Fan

The technologies used in freshwater prawn farming are basically the same as in marine shrimp farming. Hatcheries produce postlarvae, which then are grown and acclimated in nurseries before being transferred into growout ponds, where the prawns are then fed and grown until they reach marketable size. COMPAQ Presario F500 CPU Fan

Harvesting is done by either draining the pond and collecting the animals ("batch" harvesting) or by fishing the prawns out of the pond using nets (continuous operation).

Due to the aggressive nature of M. rosenbergii and the hierarchy between males, stocking densities are much lower than in penaeid shrimp farms. Intensive farming is not possible due to the increased level of cannibalism, HP Pavilion dv2310ca CPU Fan

so all farms are either stocked semi-intensively (4 to 20 postlarvae per square metre) or, in extensive farms, at even lower densities (1 to 4/m²). The management of the growout ponds must take into account the growth characteristics of M. rosenbergii: the presence of blue-claw males inhibits the growth of small males, and delays the metamorphosis of OC males into BCs. Compaq Presario C554US CPU Fan

Some farms fish off the largest prawns from the pond using seines to ensure a healthy composition of the pond's population, designed to optimize the yield, even if they employ batch harvesting. The heterogeneous individual growth of M. rosenbergii makes growth control necessary even if a pond is stocked newly, starting from scratch: HP Pavilion dv9660ef CPU Fan

some animals will grow faster than others and become dominant BCs, stunting the growth of other individuals.

The FAO considers the ecological impact of freshwater prawn farming to be less severe than in shrimp farming. SONY UDQF2PH05-AS CPU Fan

The prawns are cultured at much lower densities, meaning less concentrated waste products and a lesser danger of the ponds becoming breeding places for diseases. The growout ponds do not salinate agricultural land, as do those of inland marine shrimp farms. However, the lower yield per area means that the income per Ha is also lower and a given area can support fewer humans. SONY Vaio VGN-A17CP CPU Fan

This limits the culture area to low value lands where intensification is not required. Freshwater prawn farms do not endanger mangroves, and are better amenable to small-scale businesses run by a family.[4] However, like marine farmed shrimp, M. rosenbergii is also susceptible to a variety of viral or bacterialdiseases,[5] including white tail disease,[6] also called "white muscle disease".Toshiba G20 CPU Fan

The global annual production of freshwater prawns 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. Other major producer countries are Taiwan, Bangladesh, and Vietnam. In the United States, only a few hundred small farms for M. rosenbergii produced about 50 tonnes in 2003.[2] DELL Vostro 1510 CPU Fan

The U.S. is, though, the largest producer of farmed crayfish. In 2003, U.S. farms produced 33,500 tonnes of red swamp crawfish (Procambarus clarkii), a crayfish species native to North America.

The krill fishery is the commercial fishery of krill, small shrimp-like marine animals that live in the oceans world-wide. ACER Aspire One A150-1249 CPU Fan

The present estimate for the biomass of Antarctic krill (Euphausia superba) is 379 million tonnes.[1] The total global harvest of krill from all fisheries amounts to 150–200,000 tonnes annually, mainly Antarctic krill and North Pacific krill(E. pacifica).

Krill are rich in protein (40% or more of dry weight) and lipids (about 20% in E. superba). Their exoskeleton amounts to some 2% of dry weight of chitin. HP Pavilion dv9766ez CPU Fan

They also contain traces of a wide array of hydrolytic enzymes such as proteases, carbohydrases,nucleases and phospholipases, which are concentrated in the digestive gland in the cephalothorax of the krill.

Most krill is used as aquaculture feed and fish bait; other uses include livestock or pet foods. Only a small percentage is prepared for human consumption. Dell Vostro 3400 CPU Fan

Their enzymes are interesting for medical applications, an expanding sector since the early 1990s.

Krill are small animals, considered a type of zooplankton, and hence need to be fished with very fine-meshed plankton nets. Such nets pose several problems: they tend to clog fast, and they have a very high drag, producing a bow wave that deflects the krill to the sides. SONY Vaio VGN-SZ4MRN/B CPU Fan

Trawling must hence be done at low speeds. Additionally, fine nets are also very delicate, and the first krill nets designed exploded while fishing through the krill schools. Furthermore, fine nets increase unwanted bycatch, such as fish fingerlings, which might have unforeseen side-effects on the ecosystem, even though large krill aggregations tend to be monospecific. DELL Inspiron 1720 CPU Fan

Yet another problem is bringing the krill catch on board. When the full net is hauled out of the water, the organisms compress each other, resulting in great loss of the krill's liquids. Experiments have been carried out to pump Antarctic krill, while still in water, from the cod end of the net through a large tube on board. This method had already been used by the small fishing boats in Japanese waters; ASUS BFB0705HA CPU Fan

it increases the capture capacity and the processing rate of krill.

One of the first Antarctic krill trawlers to use this technique was the FV Atlantic Navigator, registered in Vanuatu and owned by the Norwegian-based company Aker ASA,[2] which used this technique in the 2003/04 and 2004/05 fishing seasons. HP G56-106EA CPU Fan

In these seasons, this ship alone caught 25% and 38% of the whole krill catch in CCAMLR regions.[3] The successor ship of the Atlantic Navigator, the FV Saga Sea, can fish up to about 120,000 tonnes of krill annually,[Note 1] and Aker announced plans to build more such ships.[7]

Krill must be processed within one to three hours after capture due to the rapid enzymatic breakdown and the tainting of the meat by the intestines.[8] HP Pavilion dv7-2025es CPU Fan

They must be peeled because their exoskeleton contains fluorides, which are toxic in high concentrations.

Most krill is processed to produce fish food for use in aquariums and aquacultures. The krill is sold freeze-dried, either whole or pulverized. Krill as a food source is known to have positive effects on some fish, such as stimulating appetite or resulting in an increased disease resistance. TOSHIBA Satellite L300 CPU Fan

Furthermore, krill contains carotenoids and is thus used sometimes as a pigmentizing agent to color the skin and meat of some fish. About 34% of the Japanese catch of E. superba and 50% of E. pacifica are used for fish food; the Canadian catch is used almost exclusively for this purpose.

One quarter of the Japanese catch of E. superba is used in the form of fresh frozen krill as fish bait and half the E. HP G62-a10EJ CPU Fan

pacifica catch is used as chum for sport fishing. About 43% of the Japanese catch of E. superba is processed for human consumption. The Japanese industry produces boiled, frozen krill and peeled tail meat. Other uses include krill pastes or processed krill as food additives, e.g. in the form of krill oil gel capsules. Dell MF60100V1-Q000-G99 CPU Fan

Medical applications of krill enzymes include products for treating necrotic tissue and as chemonucleolytic agents. Of the 376 krill-related patents that had been registered world-wide until 2002, 17% related to medical uses. Most of these medical patents had been registered after 1988.

Krill fishery in the Southern Ocean targets the largest species of krill existing, DELL R859C CPU Fan

the Antarctic krill (Euphausia superba), which can grow to about 6 cm (2.4 in). Fishing began in the early 1960s, when the Soviet Union launched its first experimental operations. All throughout the decade, preparatory activities were carried out, resulting in small catches of a few tens of tonnes per year. Toshiba Satellite A105-S2101 CPU Fan

Scientists mapped the locations of krill swarms to determine the best fishing grounds, and engineers developed and improved the equipment necessary to fish and process krill. In 1972, the Soviets set up a permanent fishery in Antarctic waters, landing 7,500 tonnes in 1973 and then expanding quickly. The Japanese began experimental krill fishing operation in the area in 1972 and started full-scale commercial operations in 1975. SONY Vaio VGN-FW140E CPU Fan

Krill catch increased rapidly. In the 1980s, a few additional nations started operating in the area: Poland, Chile, and South Korea. Their catches amounted to a few thousand tonnes annually; the lion's share went to the Soviet Union, followed by Japan. A peak in krill harvest was reached in 1982 with a total production of over 528,000 tonnes, of which the Soviet Union produced 93%. ACER Aspire 5730Z CPU Fan

In the following two years, production declined. It is unclear whether this was due to the discovery offluorides in the krill's exoskeleton or to marketing problems. The trade recovered quickly, though, and reached more than 400,000 tonnes again in 1987.

With the demise of the Soviet Union, two of its successor nations, SONY Vaio VPC-EB4S1E/WI CPU Fan

Russia and Ukraine, took over the operations. Russian operations and catches dwindled, and were abandoned altogether in 1993. Since then, Japan is one of the top producers, but facing stiff competition by other countries. Since 2000, the small South Korean Antarctic krill fishery has also expanded considerably. A U.S. company entered the market in 2001. HP Pavilion dv9580ed CPU Fan

The Norwegian company Aker ASA entered the business in 2003 with a ship registered in Vanuatu.

In 1982, the Convention on the Conservation of Antarctic Marine Living Resources (CCAMLR) came into force, as part of the Antarctic Treaty System. The CCAMLR was originally signed by fifteen states; as of 2004 it had 24 members. Toshiba Satellite L305D-S5934 CPU Fan

Its purpose is to regulate the fishery in the Southern Ocean to ensure a long-term sustainable development and to prevent overfishing. In 1993, the CCAMLR set forth catch quotas for krill, which amount to nearly five million tonnes per year.[11]

The annual catch of Euphausia superba since the mid-1990s is about 100–120,000 tonnes annually, SONY Vaio VGN-CR31S/P CPU Fan

i.e., about one fiftieth of the CCAMLR catch quota. Still, the CCAMLR is criticized for having defined its catch limits too generously, as there are no precise estimates of the total biomass of Antarctic krill available and there have been reports indicating that it is declining since the 1990s.[12] Plans to take up to 746,000 tonnes a year were disclosed at the 2007 meeting of CCAMLR.[13][14] HP Pavilion dv5-1210et CPU Fan

Fishing for Antarctic krill is commonly done from large stern trawlers using midwater trawls. For scientific purposes, vertical trawls using, for example, abongo net, are also employed.

The krill fishery in Japanese waters primarily targets the North Pacific krill (Euphausia pacifica), which reaches a size of about 2 centimetres (0.79 in). SONY Vaio VGN-FW465J/B CPU Fan

The annual catch is of the order of 60–70,000 tonnes. Minor fisheries for Euphausia nana (a few thousand tonnes) and Thysannoessa inermis (a few hundred tonnes annually) also exist. The fishing ground are all above the continental shelf close to the coast and at most 200 m (660 ft) deep. E. nana reaches only 1.2 cm, and T. inermis can grow to 3 cm (1.2 in). HP Envy 15 CPU Fan

E. pacifica was fished as early as the 19th century. Fishing is done with small boats. The traditional technique uses bow-mounted trawls, augmented by fish pumps since the 1980s. A bow-mounted trawl can exploit only surface swarms of krill up to a depth of about eight metres. In the 1970s, the krill fishery expanded drastically and began to use also one- or two-boat seines, HP Pavilion dv7-1190er CPU Fan

which can catch swarms as deep as 150 m (490 ft). A peak in the krill production was reached in 1992 with over 100,000 tonnes. The following year, catch regulations were enforced, and since then the annual catch has been reduced by about 30%.

Small-scale fisheries for krill also exist in other areas. In Canada, Toshiba Satellite A105-S4074 CPU Fan

fishing for E. pacifica takes place in the Strait of Georgia off British Columbia; there is a government-imposed catch limit of 500 tonnes per year. Fisheries targeting the Northern krill (Meganyctiphanes norvegica), a medium-sized krill reaching body lengths of more than 4 cm (1.6 in), as well as Tysanoessa raschii (2 cm) and T. inermis in the Gulf of St.  IBM MCF-208AM05-1 CPU Fan

Lawrence and on the Scotian Shelf have been proposed, but didn't get beyond early experimental stages. They are limited to harvesting a few hundred tonnes of krill per year, and Nicol & Foster[9] consider it unlikely that any new large-scale harvesting operations in these areas will be started due to the opposition from local fishing industries and conservation groups. IBM MCF-217PAM05 CPU Fan

The shrimp fishery is a major global industry, with more than 3.4 million tons caught per year, chiefly in Asia. Rates of bycatch are unusually high for shrimp fishing, with the capture of sea turtles being especially contentious.

The term "shrimp", as used by the Food and Agriculture Organization (FAO),  HP GB0507PGV1-A CPU Fan

covers all shrimp (Caridea) and prawns (Dendrobranchiata, comprising Penaeoidea andSergestoidea) – a group formerly known as "Natantia".[1] This nomenclature often differs from local use, in which the same species may be known by different names, or where different species may be known by the same name.

Small-scale local fishery for shrimp and prawns has existed for centuries, and continues to form a large proportion of the world's shrimp fisheries.[3] Trawling increased in scale with the introduction of otter boards, IBM MCF-217PAM05 CPU Fan

which use the flow of water to hold the trawling net open, and the introduction of steam-powered vessels, replacing the earlier sail-powered boats.[3] Both of these developments took off in the 1880s, and were soon applied to shrimp fisheries, especially following the research effort of the Norwegian marine biologist Johan Hjort.[3] HP Pavilion dv6-3385la CPU Fan

Over time, the original open skiffs, 5–8 metres (16–26 ft) long, were replaced by decked boats, to which diesel engines were added, allowing the boats to reach an average of 18 m (59 ft).

In the United States, shrimp and prawn fisheries are second only to crab fishing in terms of importance. In the northern parts of the country, cold-water shrimp are targeted, HP Pavilion tx2510us  CPU  Fan

while warm-water species are targeted along the south-eastern Atlantic coast, and in the Gulf of Mexico.[5] Most of the production is of warm-water species, but this is dwarfed by the imports of shrimp, mostly from aquaculture.[5] This has led to international controversies, with some United States fishermen accusing countries such as Brazil, China, Ecuador, India, HP G62-b55EV CPU Fan

Thailand and Vietnam of dumping shrimp on the US market, while some of the producing nations protested to the World Trade Organization about duties levied by the US in response to the inferred dumping.

Shrimp fisheries produce unusually high levels of bycatch. Before the introduction of bycatch reduction devices in the 1980s, HP Pavilion dv6-2145sf CPU Fan

shrimp fishery had a bycatch ratio (ratio of the amount of non-target species caught to the amount of the target species caught) of 4.5–5.3:1.[7] Since BRDs were introduced, the bycatch ratios may have been reduced by as much as 30%.[7] Shrimp fishing is likely to "capture more sea turtles than any other commercial fishery".HP Pavilion dv7-1120ew CPU Fan

Although the various species of the genus Acetes are not always distinguished by fishermen, collectively they form the world's largest shrimp fishery.[11][Note 3] There are fisheries for Acetes in Korea, Japan and Southeast Asia, but the vast majority of the catch is in China.[11] The total catch is likely to be grossly under-recorded, but was estimated at 664,716 t in 2005.[11] HP 538340-001 CPU Fan

Within theAsia–Pacific region, the Acetes fishery is the fourth largest fishery by weight, after hairtails, anchovies and scads.

Warm-water shrimp and prawn fisheries usually target several species,[12] and are typically monitored in terms of the catch per unit effort (CPUE), rather than the complex models used for cold-water shrimp.[13] HP 535766-001 CPU Fan

Warm-water species (mainly Penaeus setiferusPenaeus aztecus, and Penaeus duorarum) provide more than 85% of the shrimp fishery in the United States, and are caught in the Gulf of Mexico and adjacent parts of the Atlantic Ocean.[14] Bycatch is a serious problem for warm-water shrimp fisheries, with inadvertent catches of sea turtles being among the most contentious issues. HP 535442-001 CPU Fan

The most important cold-water species is the "northern prawn", Pandalus borealis,[11] which accounts for 12% of the total shrimp and prawn catch.[16] Up to 70% of the catch is landed in Canada and Greenland.[11] The price of cold-water shrimp has been in decline since the 1990s, as a result of increased shrimp farming.[17] HP 535441-001 CPU Fan

Bycatch is typically managed in cold-water shrimp trawling, and rates of bycatch are accordingly low,[7] and the capture of sea turtles is rare in cold temperate waters.[18] Bycatch is mostly reduced by the use of Nordmøre grids,[19] which reduce the numbers of cod, haddock, Greenland halibut and redfish caught during shrimp trawls.[20] HP 535439-001 CPU Fan

The Nordmøre grid was invented by the Norwegian fisherman Paul Brattøy, primarily as a means of excluding jellyfish from shrimp catches, and introduced in 1989.[19] This innovation causes a minimal reduction in the quantity of shrimp caught, but can reduce the amounts of bycatch by around 97%.[19] HP 535438-001 CPU Fan

Fisheries for cold-water shrimp using pots, the bycatch is mostly of invertebrates, including squat lobsters, crabs, molluscsand echinoderms.

Taura syndrome is one of the more devastating diseases affecting the shrimp farming industry worldwide.

Taura syndrome (TS) was first described in Ecuador during the summer of 1992. HP 533736-001 CPU Fan

In March 1993, it returned as a major epidemicand was the object of extensive media coverage. Retrospective studies have suggested a case of Taura syndrome might have occurred on a shrimp farm in Colombia as early as 1990 and the virus was already present in Ecuador in mid-1991. Between 1992 and 1997, the disease spread to all major regions of the Americas where whiteleg shrimp (Litopenaeus vannamei) is cultured. IBM 13R2760 CPU Fan

The economic impact of TS in the Americas during that period might have exceeded US$ 2 billion by some estimates.

The 1992 Ecuadorian TS epidemic occurred concurrently with an outbreak of black leaf wilt disease in banana plantations. ACER LU.S040A.067 CPU Fan

The outbreak of black leaf disease led to an increase in fungicide usage within the Taura River basin district near the city ofGuayaquil. The fungicides propiconazole (Tilt, Ciba-Geigy) and tridemorph (Calixin, BASF) used to control black leaf, ran off into nearby ponds and were responsible for the disease. ACER LU.S050B.078 CPU Fan

Analytical data demonstrated propiconazole in water, sediments andhepatopancreas tissues of shrimp harvested from affected farms in Ecuador. No other pesticides were discovered.

In January 1994, at the request of Ciba-Geigy, a workshop on Taura syndrome was held at the Aquaculture Pathology Laboratory of the University of Arizona. DELL Studio 1535 CPU Fan

Experts from several countries with expertise in shrimp and insect pathology, shrimp nutrition, toxicology, myocology, water quality and farm management participated in the workshop. Industry representatives also participated. The group developed recommendations as to the standardization of the research on TS and suggested that studies be done to evaluate whether fungicides or as-yet unrecognized agents were responsible for the syndrome. HP Pavilion dv6736nr CPU Fan

Dr. Jim Brock, the aquatic disease specialist for the State of Hawaii during this period, first demonstrated the disease could be transmitted by feeding Taura victims to healthy shrimp in early 1994. The dying test shrimp were then fed to a new set of shrimp, which was dying at the same rate. Rivers' postulates[1] were fulfilled in 1994 by Dr. Ken Hasson and co-researchers at the University of Arizona. HP Envy 15-1050ca CPU Fan

This proved the viral etiology of the syndrome. The virus was named Taura syndrome virus, often referred to as TSV. The virus is referred to by the name infectious cuticular epithelial necrosis virus (ICENV) by some authors in Latin America. Taura syndrome is a notifiable disease by the Office international des Épizooties (OIE), which reflects the serious nature and devastating impact of the disease. HP Pavilion dv7-6100et CPU Fan

Taura syndrome virus was first classified as a possible member of the family Picornaviridae based on biological and physical characteristics. It was later reclassified in the Dicistroviridae family, genus Cripavirus. It has since been reassigned to a second genus in the same family - the Aparavirus. APPLE 661-4951 CPU Fan

TSV is a 32 nm nonenveloped particle with an icosahedral morphology and a buoyant density of 1.338g/ml.[2] The genome is single-stranded positive-sense and has 10,205 nucleotides (excluding the 3' poly-A tail). The capsid consists of three major proteins: CP1 (40 kDa), CP2 (55 kDa) and CP3 (24 kDa) alongside a minor protein of 58 kDa.[3] IBM 42W2403 CPU Fan

Audelo-del-Valle in 2003 reported certain primate cell lines could be used to culture TSV. Later studies demonstrated their report was based on misinterpreted data. TSV does not appear to be a potential zoonosis. All virus amplifications require the use of live shrimp,[4] as there is no continuous cell line that supports the growth of shrimp viruses. ACER Aspire 9304WSMi CPU Fan

RNA viruses such as TSV have high rates of spontaneous mutation. These very high rates might be due to the lack of proofreading function of the RNA-dependent RNA polymerase and have resulted in the emergence of several genetic variants of the virus. As of May 2009, four genetic clusters are recognized: Belize (TSV-BZ), America (TSV-HI), Southeast Asia and Venezuela. HP 610773-001 CPU Fan

The Belize strain is considered the most virulent. Point mutations in TSV capsid proteins might provide specific isolates with selective advantages such as host adaptability, increased virulence or increased replication ability. Even small variations in the TSVgenome can result in substantial differences in virulence. IBM ThinkPad R50p 1830 CPU Fan

All TSV variants are similar in shape and size, with light variations. The average size of TSV-BZ virus particles is 32.693+/- 1.834 nm compared to TSV-HI with a size of 31.485 +/- 1.187 nm. The region of highest genetic difference is within the capsid protein CP2, with pairwise comparison of nucleotide showing a 0 to 3.5% difference amongst isolates. IBM ThinkPad T61 8898 CPU Fan

The most variations in CP2 occur at the 3'-terminal sequence; this may be because it is less constrained by structural requirements and more exposed than other regions of the protein.

TSV has been reported from virtually all shrimp-growing regions of the Americas, including Ecuador, Colombia, Peru, Brazil, El Salvador, IBM ThinkPad R50p 2889 CPU Fan

Guatemala, Honduras, Belize, Mexico, Nicaragua, Panama, Costa Rica, and Venezuela, as well as from the States of Hawaii, Texas, Florida and South Carolina.[5] Until 1998, it was considered to be a Western Hemisphere virus. The first Asian outbreak occurred in Taiwan. It has more recently been identified in Thailand, Myanmar, IBM ThinkPad R50p 1830 CPU Fan

 China,Korea and Indonesia, where it has been associated with severe epizootics in farmed Penaeus vannamei and Penaeus monodon.

The wide distribution of the disease has been attributed to the movement of infected host stocks for aquaculture purposes. This might have been helped by the highly stable nature of the virus. IBM ThinkPad R50 1829 CPU Fan

Importation of TSV-infected Penaeus vannamei from the Western Hemisphere is thought to have been the origin of the outbreak in Taiwan. This was further suggested by the genomic similarity of the Taiwan and Western Hemisphere isolates. TSV appeared in Thailand in 2003. Due to the similarities in deduced CP2 amino acids sequence and the chronology of the disease outbreaks in relation to imported stocks, IBM ThinkPad R50P CPU Fan

it is likely at least some of the Thai isolates originated from Chinese stocks.

Taura syndrome can spread rapidly when introduced in new areas. A shrimp farmer described the 1995 outbreak in Texas as "This thing spread like a forest fire... There was no stopping it. I just sat there and watched it and in a matter of three days, my shrimp were gone. Dead!" IBM Thinkpad W500 CPU Fan

TSV is known to affect many shrimp species. It causes serious diseases in the postlarval (PL), juvenile and adult stages of Penaeus vannamei. It also affects severely P. setiferusP. stylirostrisP. schmittiMetapenaeus ensisP. chinensis is highly susceptible to the disease in experimental bioassays.[7] Compaq Presario CQ41-206TU CPU Fan

There is variation within species and TSV-resistant strains of shrimp have been developed. Wild stocks are showing increased resistance, perhaps through intense natural selection. Reports of TS in the wild are limited, but in February 1995, the Mexican Fisheries Ministry reported the presence of TSV in wild-type shrimp captured on the border of Mexico and Guatemala.  SONY Vaio VPC-EB4X1E/BQ CPU Fan

As of 2007, no confirmed reports indicated TSV is infectious to other groups of decapod or nondecapod crustaceans.

In farm situations, TS often causes high mortality during the first 15 to 40 days of stocking into shrimp ponds. The course of infection may be acute (5–20 days) to chronic (more than 120 days) at the pond and farm level. HP G62-374CA CPU Fan

The disease has three distinct phases that sometimes overlap: acute, transition and chronic. The disease cycle has been characterized in detail in P. vannamei.

After the initial infection, the acute phase develops. Clinical signs can occur as early as 7 hours after infection in some individuals and last for about 4–7 days. Infected shrimp display anorexia, lethargy and erratic swimming behavior. HP Pavilion dv5-1203eg CPU Fan

They also present opacification of the tail musculature, soft cuticle and, in naturally occurring infection, a red tail due to the expansion of the red chromatophores. Mortality during this phase can be as high as 95%. The acute phase is characterized histologically by multifocal areas of nuclear pyknosis/karyorrhexis and numerous cytoplasmic HP Pavilion dv7-3131ez CPU Fan

inclusion bodies in the cuticular epithelium and the subcutis of the general body surface, all appendages, gills, hindgut, esophagus and stomach. The pyknosis and karyorrhexis give a “buckshot” appearance to the tissue and are considered pathognomonic for the disease. In severe infections the antennal gland tubule epithelium, the hematopoietic tissues and the testis are also affected. HP 052907A CPU FAN

This occurs mainly in severe infection following injection of viral particles and has not been reported from naturally infected P. vannamei. Shrimp that survive the acute stage enter a transitional stage.

Shrimp in the transitional phase show randomly distributed, melanized (brownish/black) lesions within of the cuticle of the cepahlothorax and tail region. HP 13.V1.B3403.GN CPU FAN

These foci are the sites of acute lesions which have progressed onto subsequent stages of hemocytic inflammation,[8] cuticular epithelium regeneration and healing and which might be secondarily infected with bacteria. These foci are negative for TSV by in situ hybridization (ISH) using a TSV-specific cDNA probe. Histologically, HP 13.V1.BJ195.F.GN CPU FAN

these shrimp present focal active acute lesions and the onset of lymphoid organ spheroids (LOSs) development.[9] By ISH with TSV-specific probes, a diffuse positive signal can be observed within the walls of the lymphoid organ of normal appearance with or without focal probe signals within developing LOSs. These shrimp will be lethargic and anorexic, HP 344872-001 CPU FAN

possibly because of the redirection of their energy and metabolic resources toward wound repair and recovery. If the shrimp undergo another successful moult following the transitional phase, they will cast off the melanized lesions and enter the chronic phase.

The chronic phase is first seen six days after infection and persist for at least 12 months under experimental conditions. HP 367795-001 CPU FAN

This phase is characterized histologically by the absence of acute lesions and the presence of LOS of successive morphologies. These LOSs are positive by ISH for TSV. A low prevalence of ectopic spheroids can also be observed in some cases. LOSs are not by themselves characteristic of TSV infection and can be found in other viral diseases of shrimp such as lymphoid organ vacuolization virus (LOVV), HP 384622-001 CPU FAN

lymphoid parvo-like virus (LPV), lymphoid organ virus (LOV), rhabdovirus of penaeid shrimp (RPS) andyellowhead virus (YHV). Diagnosis of the disease during the chronic phase is problematic, as shrimp do not display any outward signs of the disease and do not show mortality from the infection. Survivors may become carriers for life.[10] HP 3MLX6TATPH0 CPU FAN

Shrimp with chronic TSV infection are not as vigorous as uninfected shrimp, as demonstrated by their inability to tolerate a salinity drop as well as uninfected shrimp.[11] A 2011 study by Laxminath Tumburu looked at the relationship between an environmental stressor (pesticide Endosulfan) and Taura syndrome virus (TSV) and their interactions on the susceptibility and molting of marine penaeid shrimp L. HP 3MLX8TATP20 CPU FAN

vannamei and found the interference of endosulfan-associated stress led to increasingly higher susceptibility at postmolt stage during the acute phase of the TSV disease cycle.

The most likely route for transmission of TSV is cannibalism of dead infected shrimp. The virus can be spread from one farm to another by seagulls and aquatic insects.[13] HP 3MLX8TATP40 CPU FAN

Infectious TSV has been found in the feces of laughing gulls (Larus atricilla) that fed on infected shrimp during an epizootic in Texas. Controlled laboratory studies have documented that TSV remains infectious for up to one day after passage through the gut of white leghorns chicken (Gallus domesticus) and laughing gulls.[14] Although, vertical transmission is suspected this has not been experimentally confirmed.[15] HP 3MLX9TATP70 CPU FAN

Shrimp surviving a TSV infection are lifelong carriers of the viruse and are a significant source of virus for susceptible animals. It has been hypothesized that TSV was introduced to Southeast Asia with chronically infected shrimp imported from the Western Hemisphere. The ability of TSV to remain at least partly infectious after one or several freeze-thaw cycles might be a contributing factor facilitating its spread in the international commerce of frozen commodity products. HP 407862-001 CPU FAN

Mechanisms by which infected frozen shrimp could spread the virus include: reprocessing of shrimp at processing plants with release of infectious liquid wastes, disposal of solid wastes in landfills where seagulls could acquire the virus and then spread it, the use of shrimp as bait by sport fishermen and the use of imported shrimp as fresh food for other aquatic species. HP 414226-001 CPU FAN

A presumptive diagnosis of acute TSV infection can be established by the presence of dead or dying shrimp in cast nets used for routine evaluation. Predatory birds are attracted to diseased ponds and feed heavily on the dying shrimp. The unique signs of infection caused by TS, such as the cuticular melanized spots, can provide a strong presumptive diagnosis, HP 418409-001 CPU FAN

but care must be taken as these can be confused with other diseases, such as bacterial shell disease.[Note 1] In general pathognomonic histopathological lesions are the first step in confirmatory diagnosis. Discrete foci of pyknotic and karyorhectic nuclei and inflammation are seen within the cuticular tissues. The lymphoid organ might display spheroids, but is otherwise unremarkable. HP 431312-001 CPU FAN

The genome of the virus has been cloned and cDNA probes are available for diagnosis. Reverse transcriptase polymerase chain reaction (RT-PCR) methods have been developed for detection of TSV and are very sensitive. Real-time techniques allow for quantification of the virus. The IQ2000TM TSV detection system, a RT-PCR method, is said to have a detection limit of 10 copies per reaction.[17] HP 434678-001 CPU FAN

RNA-based methods are limited by the relative fragility of the viral RNA. Prolonged fixation in Davidsons' fixative might result in RNA degradation due to fixative-induced acid hydrolysis. An alternative for virus detection is the use of specific monoclonal antibodies (MAbs) directed against the relatively stable proteins in the viral capsid. HP 441137-001 CPU FAN

Rapid diagnostic tests using MAbs are now in common use for white spot syndrome virus and are being marketed under the commercial name of Shrimple.[18] Similar tests for TSV, yellowhead virus and infectious hypodermal and haematopoietic necrosis virus are currently under development. HP 448016-001 CPU FAN

Management strategies for the disease have included raising more resistant species such as the Western blue shrimp (Penaeus stylirostris) and stocking ofspecific pathogen free (SPF) or specific pathogen resistant (SPR) shrimp. Relatively simple laboratory challenges can be used to predict the performance of selected stocks in farms where TSV is enzootic. HP 450933-001 CPU FAN

The resistant shrimp lines currently raised have reached nearly complete resistance to some TSV variants and further improvement due to breeding for TSV-resistance is expected be minor for these variants.[19] Significant improvements in TSV survival were made through selective breeding despite low to moderate heritability for this trait. HP 456605-001 CPU FAN

A management strategy used to reduce the impact of TS has been the practice of stocking postlarval shrimp at increased stocking density. Following this strategy, farms would experience mortality due to TS at an early stage of the production cycle, before substantial feeding had begun and the surviving shrimp would be resistant to further TSV challenges. HP 480481-001 CPU FAN

Other techniques used with limited efficacy have been the polyculture of shrimp with tilapia [20] and maintenance of near-optimal water quality conditions in the grow-out ponds with reduction of organic loading. Transgenic shrimp expressing an antisense TSV coat protein (TSV-CP) exhibited increased survival in TSV challenges. HP 486799-001 CPU FAN

The public perception of transgenic animals, as well as current technical limitations, limit the use of transgenic animals as a mean of disease control. HP 486844-001 CPU FAN,HP 489126-001 CPU FAN,HP 493001-001 CPU FAN

Partager cet article

Repost 0
Published by batterys
commenter cet article