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The introduction of Penaeus vannamei and P. stylirostris into the Asia-Pacific region

Simon Funge-Smith
and Matthew Briggs

Background

In 2000, global aquaculture production reached 45.71 million metric tonnes (mmt) with a value of US$ 56.47 thousand million. This represented an increase in production of 6.3% by weight and 4.8% by value over the previous year. Although crustaceans represented only 3.6% of total production by weight, they comprised 16.6% of total global aquaculture by value in 2000. Despite being affected by serious disease outbreaks in both Latin America and Asia, the annual percent rate of growth (APR) of the shrimp sector grew by 6.8% by weight between 1999 and 2000. These growth rates are still high relative to other food production sectors, however in terms of growth, shrimp production has decreased to more modest levels over the last decade (averaging 5%) relative to the double-digit growth rates which were observed during the 1970's (23%) and 1980's (25%).

Marine shrimp continued to dominate crustacean aquaculture, with three major species accounting for over 86% of total shrimp aquaculture production in 2000 (the giant tiger prawn, Penaeus monodon; the fleshy prawn, P. chinensis; and the whiteleg shrimp, P.vannamei) (Figure 1). Whilst the giant tiger prawn only ranked 20thby weight in terms of global aquaculture production by weight in 2000, it ranked first by value at US$4047 billion.

Natural Range of P. vannamei and P. stylirostris

Penaeus vannamei and P. stylirostris both originate on the Western Pacific coast of Latin America from Peru in the South to Mexico in the North. P. vannamei is native to the Pacific coast of Mexico, Central and South America as far south as Peru, in areas where water temperatures are normally >20°C throughout the year (Wyban and Sweeney, 1991; Rosenberry, 2002). It is not currently known whether there is one population throughout the year or if isolated populations exist, although there do appear to be differences between stocks from various areas under culture conditions.

Figure 2. Exports os shrimp (mt) from Ecuador 1979–2002 and environmenta/disease events

P. stylirostris is native to the Pacific coast of Central and South America from Mexico to Peru, occupying the same range as P. vannamei, but with higher abundance, except for in Nicaragua at the peak of the range of P. vannamei (Rosenberry, 2002). It has recently been demonstrated that there are at least 6 morphologically and genetically distinct populations of P. stylirostris in the Gulf of California, Mexico alone (Lightner et al., 2002), raising the probability that there will be variations in their suitability for aquaculture.

The culture industry for P. stylirostris in Latin America is largely confined to Mexico, but P. vannamei has become the primary cultured species in Latin America from the USA to Brazil over the past 20–25 years. Total production of this species in the Americas probably amounted to some 200000 mt, worth $1.2 billion in 2002.

P. vannamei was introduced into Asia experimentally from 1978–1979, but commercially only since 1996 into Mainland China and Taiwan province of China, followed by most of the other coastal Asian countries in 2000–2001. Experimental introductions of SPF “supershrimp” P. stylirostris have been made into various Asian countries since 2000, but the only country to develop an industry to date has been Brunei.

Worldwide movements and introductions

The use of exotic animal species to increase food production and income has a long history and has been an established practice since the middle of the 19th Century. Controversy over the use of exotic species arises from the many highly publicised and spectacular successes and failures.

FAO statistics show that aquaculture development has been the primary reason cited for most introductions, accounting for 40% of all cases, and that the number of introductions (65% intentional) has increased exponentially since 1940. Most of these introductions are of fish, with only 6% or 191 records being of crustaceans. Such movements have been facilitated by recent advances in transport, which have made large-scale movements of many species increasingly easy. They are also directly related to the rapid global development of the aquaculture industry and the demand for new species to culture (FAO database of introduced aquatic species - DIAS, Fegan et al., 2001).

With regard to Penaeid shrimp, the first experimental movements began in the early 1970s, when French researchers in Tahiti developed techniques for intensive breeding and rearing of various exotic Penaeid species including P. japonicus, P. monodon and later P. vannamei and P. stylirostris. Later, in the late 1970s and 1980s, P. vannamei and P. stylirostris were translocated from their natural range on the Pacific coast of Latin America from Mexico to Peru. From here, they were introduced to the North-Western Pacific coast of the Americas in the USA and Hawaii, and to the Eastern Atlantic coast from Carolina and Texas in the North through Mexico, Belize, Nicaragua, Colombia, Venezuela and on to Brazil in the South. Most of these countries now have culture industries for these species. P. monodon and P. japonicus were also experimentally introduced in the 1980s and 1990s from Asia to various Latin American countries including the USA, including Hawaii (where SPF populations have been established), and Ecuador and Brazil, where introductions were not successful.

Table 1. Importation of P. vannamei and P. stylirostris in Asian countries

Notes: Cultured species:
C = P. chinensis,
M = P. monodon,
Me = P. merguiensis,
I = P. indicus,
S = P. stylirostris,
J = P. japonicus,
P = P. penicillatus,
Ma = Macrobrachium rosenbergii

Source/Broodstock Imports:
Hi = Hawaii,
Ti = Taiwan province of China,
Ch = Mainland China,
Mx = Mexico,
Th = Thailand,
Tx = Texas,
P = Panama

More recently, experimental introductions of P. vannamei to Asia began in 1978/79 to the Philippines (FAO correspondent) and in 1988 to Mainland China (FAO correspondent). Of these first trials, only Mainland China maintained production and started an industry. However, beginning in 1996, P. vannamei was introduced into Asia on a commercial scale. This started in Mainland China and Taiwan province of China and quickly spread to the Philippines, Indonesia, Viet Nam, Thailand, Malaysia and India. A summary of the introduction of P. vannamei and P. stylirostris to Asia is presented in Table 1.

P. vannamei has been introduced and farmed in Asia since the mid 1990s, with production in Mainland China being particularly significant. There have been several reasons for the introduction and subsequent movement; apparent availability of specific pathogen free (SPF) stocks; perceived differences in susceptibility to WSSV from P. monodon; shortage of P. vannamei in the international market (mainly USA) caused by reduced production in Latin America, and the relative ease with which animals could be cultured and bred in captivity.In some countries, P. vannamei culture has been promoted by some private sector suppliers as being tolerant or resistant to WSSV, leading to introductions based on a mistaken belief that they are safe.

China has a large and flourishing industry for P. vannamei, with Mainland China producing >270000 mt in 2002 and an estimated 300000 mt (71% of total shrimp production) in 2003, which is higher than the current production of the whole of Latin America. Other Asian countries with developing industries for this species include Thailand (120000 mt estimated production for 2003), Viet Nam and Indonesia (30000 mt estimated for 2003 each), with Taiwan province of China, the Philippines, Malaysia and India also producing thousands of tonnes each.

Total production of P. vannamei in Asia was approximately 316000 mt in 2002, and it has been estimated that this will increase to nearly 500000 mt in 2003, which would be worth some $4 billion on the export market. However, not all the product is exported outside of the region and a large local demand exists in some Asian countries.

It is now evident that P. vannamei is farmed and established in several countries in East, Southeast and South Asia and is playing a more significant role in shrimp aquaculture production. On the other hand, it is also evident that viruses previously confined to Latin America, such as TSV are taking a toll within P. vannamei shrimp aquaculture in many countries in Asia and there have also been reports of “runt deformity syndrome” (RDS) caused by IHHNV, which is endemic in P. monodon in the region.

The overall performance of P. vannamei as a candidate species within shrimp aquaculture sector is still unclear. The knowledge and understanding of the social, economic, and environmental impacts of introduction of this species into Asia is far from adequate. It is uncertain how this species will behave and perform in the region, as a newly introduced species, and what impacts it will bring to the regional economy, environmental sustainability, rural livelihoods and regional biodiversity. Therefore, it is recognized that a review/study towards assessing the introduction and impacts of P. vannamei in the Asia-Pacific region is timely.

Table 2. Summary of advantages and disadvantages of the culture of P. vannamei and P. stylirostris over P. monodon in Asia

Table 3. Estimated Production of all shrimp and P. vannamei in Asian countries

Note : all data for 2003 is estimated

Stocks of IHHN-resistant P. stylirostris based on the Tahiti strain were also introduced into the region in recent years. Although these stocks did not become as widely distributed as P. vannamei, some stocks of P. stylirostris remain and there may be some interest in this species should RDS become a limiting factor.

Advantages and disadvantages of P. vannamei and P. stylirostris

There are many reasons for the introduction of P. vannamei and P. stylirostris outside of their natural range. Despite the presence of various international, regional and country-specific regulations, the private sector (and/or government) often initiate introductions due to problems with the culture of their indigenous species and the perceived (rightly or wrongly) production benefits of the exotic species. There may also be marketing advantages and a desire to expand, intensify and/or diversify aquaculture systems. Additionally, the improved transportation efficiency available recently has removed some old limitations and encouraged international trade in exotic species. The advantages and disadvantages of P. vannamei and P. stylirostris as compared to native species, specifically P. monodon are shown in Table 2.

The main reason behind the importation of P. vannamei to Asia has been the poor performance, slow growth rate and disease susceptibility of the major indigenous cultured shrimp species, P. chinensis in China and P. monodon virtually everywhere else. Cultured shrimp production in Asia has been characterised by a series of outbreaks of disease caused by viral pathogens which have caused significant losses to the culture industries of most Asian countries over the past decade. These diseases have not been confined to single countries but have spread throughout shrimp culture regions apparently as a result of transfers of infected stock. It was not until the late 1990s, spurred by the production of the imported P. vannamei, that Asian (and therefore world) production levels have begun to increase again.

Despite the problems with disease transfer, P. vannamei (and P. stylirostris) does offer numerous advantages over P. monodon for the Asian shrimp farmer. These are largely associated with the ability to close the life cycle and produce broodstock within the culture ponds. This relieves the necessity of returning to the wild for stocks of broodstock or PL and permits domestication and genetic selection for favourable traits such as growth rate, disease resistance and rapid maturation. Through these means, domesticated stocks of SPF and SPR shrimp have been developed and are currently commercially available from the USA.

Other specific advantages include, rapid growth rate, tolerance of high stocking density, tolerance of low salinities and temperatures, lower protein requirements (and therefore production costs), certain disease resistance (related to SPR stocks), and high survival during larval rearing, and some marketing advantages. However, there are also disadvantages, including their acting as a carrier of various viral pathogens new to Asia, a lack of knowledge of culture techniques (particularly for broodstock development) in Asia, smaller final size and hence lower market price than P. monodon, need for high technology for intensive ponds, competition with Latin America for markets, and a lack of support for farmers due to their often illegal status.

Since it is clear that P. vannamei culture is already established and growing fast in the Asian region (Table 3), it is important that informed decisions regarding these advantages and disadvantages and appropriate action needs to be taken. This would ideally develop with a close dialogue between government and private sector as well as other concerned organisations.

Threats and risks of introducing exotic shrimp species

Unregulated trans-boundary movement of aquatic animals can lead to substantial economic and environmental impacts through the transfer diseases and pathogens. Trans-boundary pathogen transfers in newly imported species often result in establishment of infection in naturally susceptible indigenous hosts and may lead to the adaptation of pathogens to a new range of hosts.Due to their inherent genetic variability, rapid rate of replication, and common occurrence as low-level latent infections in apparently healthy animals, the transfer of viral pathogens is of particular concern.However, during the past decade, powerful DNA-based molecular tools have become available to trace the origins and spread of infections in animal populations and monitor viral adaptation to new hosts.These methods have been widely applied to infections in terrestrial animals and humans (e.g. foot-and-mouth disease in Europe, West Nile virus in the USA, HIV globally) but there has been quite limited application to aquatic animals. This approach, which has become known as molecular epidemiology, uses selected genetic markers to distinguish individual viral isolates.Accumulating mutations that occur as viruses spread through animal or human populations can be used to determine the relationship between isolates and the patterns of pathogen spread.

Viral disease

The Taura Syndrome Virus (TSV), which was initially identified on P. vannamei shrimp farms near the Taura River in Ecuador in early 1992, caused severe production and economic losses to the shrimp sector in the Americas, and remains as a major constraint to the sectoral development. Similarly, White Spot Syndrome Virus (WSSV), which was initially identified on P. monodon in Mainland China and Taiwan province of China, severely affected the Asian shrimp industry, and subsequently spread to Americas affecting P. vannamei production systems.

Table 4. Hatchery and PL production for all shrimp and P. vannamei in Asian countries

Note: all data is for 2002

Although there is no reported evidence yet that TSV has spread to the major indigenous farmed shrimp species (P. monodon and P. chinensis) there has been a report of infection in wild metapenaeid shrimp in Taiwan province of China and an accompanying genetic adaptation of the virus. As a highly mutable RNA virus, TSV is particularly suitable for molecular epidemiological studies that, at this early stage of pathogen establishment, could be applied to trace the spread, adaptation and impact of the virus on indigenous farmed and wild crustaceans in the region. The methodology could also be applied to the detection and monitoring of other pathogens, particularly viruses that may be introduced with the species.

In Asia, first Yellowhead Virus (YHV) from 1992 and later White Spot Syndrome Virus (WSSV) from 1994 caused continuing direct losses of approximately $1 billion per year to the native cultured shrimp industry. In Latin America, first Taura Syndrome Virus (TSV) from 1993 and later, particularly, WSSV from 1999 caused direct losses of approximately $0.5billion per year after WSSV (Figure 2). Ancillary losses involving supporting sectors of the industry, jobs, and market and bank confidence put the final loss much higher.

It is widely believed that these three most economically significant viral pathogens (and a host of other pathogens) have been introduced to the Asian and Latin American countries suffering these losses through the careless introduction of live shrimp stocks. Except for China, most Asian countries have legislated against the introduction of P. vannamei due to fears over the possibility of importing new pathogenic viruses and other diseases from Latin America to Asia.

Many governments have allowed importation of supposedly disease free stocks that are available for this species from the USA. The encouraging trial results, the industry-perceived benefits, including superior disease resistance, growth rate and other advantages, allied with problems controlling the imports from other countries, has lead to the widespread introduction of this species to Asia, primarily by commercial farmers. Unfortunately, importation of cheaper, non-disease free stock has resulted in the introduction of serious viral pathogens (particularly TSV) into a number of Asian countries, including Mainland China, Taiwan province of China, Thailand and Indonesia, and possibly more. There are now many hatcheries established in Asia that are producing postlarvae for stocking (Table 4), although the original sources of the stock and their current health status are quite uncertain. What can be assumed is that many of the hatcheries are not able to maintain their stocks as SPF and invariably they become infected with local virus disease and quite possibly with the disease that are typical to the species when in South America (e.g. Taura). This is partly due to private sector hatcheries being unaware of the requirements for maintaining clean stocks and partly dues to corner cutting due to the rising demand for postlarval P. vannamei.

Biodiversity and impacts on wild stocks

Although TSV does not seem to have affected the indigenous cultured or wild shrimp populations, insufficient time and research has been conducted to prove this. TSV is also a highly mutable virus, capable of mutating into more virulent strains, which are able to infect other species. In addition, other viruses probably imported with P. vannamei, for example a new LOVV-like virus, have been implicated in actually causing the slow growth problems currently being encountered with the culture of the indigenous P. monodon. There remain many unanswered questions regarding the possible effects of introduced species on other cultured and wild shrimp populations in Asia.

At present there is still no available information regarding whether P. vannamei has established in the wild and if so, the effect of its interaction with existing crustacean species. For this reason there has been caution on the part of many Asian governments. However, this caution is not shared by the private sector, which has been bringing in stocks of illegal and often disease carrying P. vannamei into Asia from many locations. The commercial success of these introductions, despite disease problems has allowed the development of substantial culture industries for these species within Asia, so that there is effectively little ability to control the importation of P. vannamei and development of this new feature of the cultured shrimp sector in Asia.

International efforts and the history of import control.

The introductions of P. vannamei to non-native areas of the Americas and lately to Asia have had a significant positive effect on the production capacities of the countries involved. This is probably the first time that this has ever been recorded with cultured shrimp. Despite the establishment of viable shrimp culture in many countries with this species, there are potential negative impacts that are emerging.

SPF “supershrimp” P. stylirostris have also been experimentally introduced to many Asian countries (including Brunei, Taiwan province of China, Myanmar, Indonesia and Singapore) from secure breeding facilities in Mexico and the US. These introductions began in 2000, but have yet to make a major impact on the culture industries in those countries (with the exception of a small industry in Brunei), but without notable problems so far. P. stylirostris was also introduced into Thailand and Mainland China in 2000, but has yet to make much impact there either.

Although incompletely understood, it is now clear that many of the introductions of trans-boundary species have also been responsible for the introduction, establishment and spread of thousands of pathogen (viruses, bacteria and fungi) and parasite species into new geographic areas and hosts. Once established in natural waters (and often aquaculture facilities) and hosts, such pathogens are almost impossible to eradicate. In most cases, fishery managers and governments have not properly considered pathogen transfer when contemplating trans-boundary movements of aquatic animals, or have been slow to react to such introductions directly by the private sector either with or without approval.

With proper planning, it may have been possible to avoid introduction of these pathogens and there now exist a number of international codes of practice and guidelines to assist this process. These include international efforts lead by:

• the World Trade Organization (WTO);

• the International Council for the Exploration of the Sea (ICES);

• the Office International des Epizooties (OIE);

• the Food and Agriculture Organization of the United Nations (FAO) via the Code of Conduct for Responsible Fisheries (CCRF);

• regionally through the latest initiative is the FAO/NACA Regional Technical Cooperation Program (TCP/RAS 6714(A) and 9605(A)) “Assistance for the Responsible Movement of Live Aquatic Animals”, which led to the Asian Technical Guidelines on Health Management for the Responsible Movement of Live Aquatic Animals.

Direct, involuntary importation of new pathogens with their imported hosts has been shown to have even less quantifiable problems including transfer of new strains of established pathogens specific to the host, the potential for interbreeding with, and displacement of, native species and unknown effects on the genetic diversity and ecology of native fauna. Each of these has the potential to cause unexpected and far-ranging adverse effects on host populations and commercial and sport fisheries, with accompanying severe socio-economic impacts on human populations.

Private sector initiatives

In some countries, the private sector has adopted best management practices (BMPs), which have helped prevent on-farm disease problems. Although governments have also assisted these efforts through the development of expertise, infrastructure and capacity for health management, shrimp culture and capture fisheries in most countries remain vulnerable to further introductions of trans-boundary diseases. There is much further work that can be done however, and this report includes recommendations as to what this might comprise.

The recent publication of a number of codes of conduct and management guidelines (BMPs) for the trans-boundary importation of exotic shrimp and their subsequent culture by amongst others, the WTO, ICES, FAO, the OIE, NACA, ASEAN, SEAFDEC and the GAA have clearly defined most of the issues involved. With the availability of SPF and SPF/SPR stocks of P. vannamei and P. stylirostris from the Americas, Asia has had the opportunity to decide whether to responsibly undertake such importations for the betterment of their shrimp culture industries and national economies, whilst avoiding the potential problems with viral diseases and biodiversity issues. However, a number of factors are described to have prevented this ideal situation from manifesting. Although many of the potential problems involved with trans-boundary movements of shrimp and their viral passengers is as yet unknown, the Asian governments must take responsibility for legislating control over this industry.

World Trade Organization (WTO)

Trade issues are governed under the terms of the World Trade Organization (WTO), the legal and institutional basis for the international trading system. The main objectives for the agreement were to ensure access to markets, promote fair competition and encourage development and economic reform. Aquacultural issues are covered specifically in the “Agreement on the Application of Sanitary and Phytosanitary Measures” (SPS, 1995) and the “Agreement on Technical Barriers to Trade” (TBT).

The SPS agreement attempts to prevent non-tariff trade barriers, based on harmonized international standards, guidelines or recommendations where they exist. However, individual governments may take more stringent measures, provided they have scientific justification (i.e. following an import risk assessment), or if it is shown that international standards do not provide sufficient risk protection. Problems with harmonization of standards may arise if for example, an importing country refuses permission to import product from a country with a new or notifiable viral disease and the exporting country does not have the mechanism to ensure the product is free from the virus. Under these circumstances, the WTO has agreed to help the exporting country with its testing procedures. Settlement of disputes bilaterally is encouraged, but the WTO has its own procedures and impartial bodies are available if this is not possible (Fegan, 2000).

Office International des Epizooties (OIE)

The Committee of Sanitary and Phytosanitary Measures is linked to the Paris-based Office International des Epizooties (OIE) that sets the international standards for animal health measures. Since 1988, in the area of aquatic animal health the OIE has the Fish Disease Commission (FDC) which is responsible for informing governments of the worldwide aquatic disease situation, coordinating surveillance and control measures possible, and harmonizing regulations for trade amongst member countries. The recently introduced standards for aquaculture are currently limited by the lack of knowledge regarding aquatic disease problems. However, the OIE is continually updating two important documents for aquatic animal health: the International Aquatic Animal Health Code (2002) and the Diagnostic Manual for Aquatic Animal Diseases (2000), which are available free of charge on the OIE website at http://www.oie.int and new versions are due to appear at the end of July, 2003.

International Council for the Exploration of the Sea (ICES)

A code of practice for introductions of non-indigenous marine organisms was set by the International Council for the Exploration of the Sea (ICES) in 1973 and revised in 1994 (ICES,1995). These codes had recommendations in the following areas: Recommended procedures for deciding on importations of new species; Recommended actions once the introduction has been approved; Encouragement for prevention of unauthorized introductions; and recommended procedures for introduced or transferred species already under commercial cultivation.

Food and Agriculture Organization of the United Nations (FAO)

FAO released a voluntary, but partly internationally legal Code of Conduct for Responsible Fisheries (CCRF) during the FAO Conference of 1995 (FAO, 1995). The CCRF was the result of four years of work following the International Conference on Responsible Fishing in Cancun, Mexico in May, 1992.

Article 9 of the code covers aquaculture development and Article 9.3.3 states that: “States should, in order to minimize risks of disease transfer and other adverse effects on wild and cultured stocks, encourage adoption of appropriate practices in the genetic improvement of broodstock, the introduction of non-native species, and in the production, sale and transport of eggs, larvae or fry, broodstock or other live materials. States should facilitate the preparation and implementation of appropriate national codes of practice and procedures to this effect”.

FAO further issued the “FAO Technical Guidelines for Responsible Fisheries No. 5: Aquaculture Development” in 1997 to provide general advice in support of Article 9 of the CCRF (FAO, 1997).

Asia Regional Initiatives (NACA & SEAFDEC/ASEAN)

Based on Article 9.3.3 of the FAO CCRF, a set of regional guidelines were issued by FAO/NACA in 2000, and called the “Asia Regional Guidelines on Health Considerations for the Responsible Movement of Live Aquatic Animals”. These guidelines were developed through three years of awareness raising and consensus building and were adopted by 21 participating countries in the Asia-Pacific region in Beijing in June, 2000.

The guidelines were further adopted by ASEAN Fisheries Working Group in Bali in 2001 as an ASEAN policy document and endorsed by the ASEAN/SEAFDEC Millennium Conference on Fish for People in 2000 in Bangkok (FAO, 2000, NACA/FAO, 2001, SEAFDEC, 2001).

Country level initiatives to control or restrict importation

Despite the existence of these codes, protocols and guidelines, the government and particularly the private sector in both Asia and Latin America continue to introduce new species with little consideration of potential disease consequences. They have thus generally been caught unprepared for the recent epizootic outbreaks involved with shrimp trans-boundary movements. Additionally, their immediate responses have been largely ineffective in preventing or reducing disease losses which may exceed $1 billion/year in direct production losses worldwide, and considerably more in total. Countries which have actively enforced importation bans, with some success include:

• Brazil, Venezuela and Madagascar (who have so far managed to exclude WSSV and YHV)

• Hawaii and the continental United States, who have managed to eradicate WSSV from their culture industry

• the Philippines, who managed to delay the onset of WSSV by 4–5 years (compared to the rest of Southeast Asia), but do have non-SPF P. vannamei despite a ban, and

• Sri Lanka, who have still not allowed even experimental importation of P. vannamei, for fear of TSV.

Reasons for the lack of success of regulations

Problems with shrimp import limitations

That the numerous codes and guidelines have been largely ineffective at preventing the spread of exotic shrimp and their viral diseases throughout the world is quite apparent. The sheer scale of the cultured shrimp industry and the fact that shrimp are not usually covered by existing livestock legislation on movements gives plenty of gaps for such movements to take place. The reasons for movements are varied and include the following:

Producer driven importation

In many cases, even though governments have implemented guidelines or laws regarding the importation of trans-boundary shrimp species, the private sector has gone ahead with such imports through smuggling, non-disclosure and exploitation of a lack of government control over such importation. Thus, although there may be good reasons for limiting imports and regulations in place, these have little chance of success in limiting imports unless the private sector can be convinced of their validity and importance.

Perception of benefits of introduced species

The largely private sector-led introductions are done, whether or not official restrictions are in place, due to the perceived benefits offered by the introduced species. Thus, in the case of P. vannamei introductions into Asia, the current perceptions that: P. vannamei are more disease resistant than the indigenous species (P. monodon and P. chinensis), SPF broodstock can be purchased that are free from disease, and that they are more able to tolerate high density, often low-salinity culture, are the main driving forces behind their introduction. Whether these perceived benefits (Table 2) are true or not is often irrelevant, particularly when Asian shrimp farmers are struggling to make money using their traditional native species. In this case, as has been seen in virtually all Asian shrimp-producing countries in the past few years, the perception of the private sector is that the potential advantages outweigh the disadvantages and so the importation are made.

Whether this perception is correct or not remains unproven. On the positive side, the Asian P. vannamei culture industry has seen a rapid expansion in the last few years, so that production of P. vannamei has surpassed that of traditional native cultured species in Mainland China, is rapidly approaching that level in Taiwan province of China and Thailand, and is gaining increasing importance in Viet Nam and Indonesia (see Table 3). The generally downward trend in Asian shrimp production during the 1990s, due largely to disease problems with P. monodon and P. chinensis, has thus now been reversed with the introduction of the relatively more tolerant P. vannamei.

On the negative side, the introduction of P. vannamei into Asia has been accompanied by the importation of various viruses, including TSV (already causing losses in Mainland China, Taiwan province of China and Thailand) and LOVV (possibly responsible for the slowing growth rate of P. monodon) and probably others. The long term effects of these viruses is unknown, but precedents from introductions of shrimp and their viruses from Asia to Latin America (i.e. IHHNV in 1981 and WSSV in 1999) are known to have resulted in severe setbacks to the shrimp culture industry and the socio-economic status of many countries. Additionally, the associated impacts of trans-boundary introductions of shrimp have unknown, but possibly serious consequences for wild shrimp populations and genetic diversity.

Recommendations for control of movement and culture of shrimp

Since it is clear that the majority of Asian countries have already introduced P. vannamei (either legally or illegally) to some extent, there is now some determination to try and ensure that any negative impacts are minimized.

Some countries are considering enforcing their official bans and destroying all stocks found within their borders (i.e. the Philippines and Malaysia). Short of this difficult (and perhaps legally unenforceable) procedure, the species, and in most cases, its attendant viruses, will remain in most countries.

A more pragmatic approach would be the investigation and elimination of all stocks infected with known pathogens, followed by an opening of the borders only to certified disease-free stocks. This assumes that the testing of stocks for import and the necessary controls of this would be strengthened, since at the moment it is the inability to effectively control imports which has allowed the introductions so far. This approach at least offers a working solution to the reality that P. vannamei is already present in many countries and being cultured at significantly economic levels in several. This also allow countries to take advantage of the potential benefits offered with this exotic species and would encourage a more responsible approach to the issue of shrimp movements and disease in the region, what is certain, is that blanket bans on the importation of species (such as P. vannamei) which are desired by the commercial sector are ineffective at preventing their introduction, under the current conditions in Asia.

Many recommendations regarding the health implications of the importation of exotic shrimp species (and their attendant pathogens), and their sustainable culture have recently been published. The following list draws heavily from the review made on the management strategies for major diseases in shrimp culture, based on a workshop held in Cebu, Philippines in 1999 (WB/NACA/WWF/FAO, 2001). The recommendations have been modified to focus on the issues involved with the trans-boundary importations of P. vannamei and P. stylirostris in Asia:

Legislation, Policy and Planning

• Develop improved legal frameworks, monitoring systems and enforcement capabilities to control and register importation and culture of exotic shrimp species.

• Increase interaction between planners, policy makers, industry and other stakeholders to discuss strategies (and their application) for practical approaches to environmentally friendly and sustainable farming of exotic shrimp species.

• Recognise in legislation the differences between “soft laws”, codes and guidelines, and regional or international agreements and WTO “hard laws”.

• Legislate penalties for beaches of legislation or quarantine and illegal activities such as smuggling, examine the issue of liability.

• Develop and/or apply “best practices” for management of the shrimp industry based on continuous refinements of the FAO CCRF and similar guidelines on aquaculture development. This should include incorporation of quality assurance programmes (HACCP) into all aspects of the shrimp culture system.

• Develop government infrastructure and industry liaison and registration of aquaculture facilities, so that codes of practice can be developed and followed, certifications or accreditation made, expertise in disease control identified and communication and awareness raised for the benefit of both parties.

• Begin to regionally harmonize and implement Import Risk Analysis (IRA) to help prevent disease transmission. Training officials in the IRA process should be given priority.

• Implement, and if necessary, design, environmental Impact Assessments (EIA) that take account of disease transmission issues with imported species.

• Formulate national policies recognizing the importance of shrimp farming as a contributor to national development and assisting its development.

• Formulate plans for comprehensive shrimp health management strategies using existing and novel approaches to correct problems in the environment, animal and pathogen.

• Develop contingency plans and provide financial, technical and educational assistance for farmers suffering from disease outbreaks.

• Enforce coastal area management regulations of relevance to shrimp farming.

• Critical analysis of approval process for shrimp farms farming exotic species.

Regional and International Cooperation

• Member states must advise OIE of any outbreaks of notifiable pathogens.

• Link national diagnostics and disease control systems with other countries' networks to strengthen regional cooperation.

• Establish a regional disease information network/website and a timely disease reporting system.

• Organize regional annual meetings and workshops on shrimp health management for dissemination of information.

• Establish data base of facilities offering certified disease-free SPF and resistant SPR stocks.

• Give priority to collaboration between Latin American and Asian regions for cross-fertilization of ideas.

• Recognise and identify the roles and inputs of NGOs.

Disease Management Issues

• Establish national reference pathology labs to inter-calibrate with, and assure the quality of, private disease labs, and collaborate with the existing OIE reference labs.

• Initiate Quality assurance programmes, including standardization of techniques and training in disease diagnosis labs to ensure their utility in the control of disease transmission.

• Require that all facilities exporting shrimp have a minimum 2 year disease free status, are certified as such and can submit independent, qualified certification of their status.

• Submit properly collected samples of imported shrimp to certified disease diagnosis laboratories for assurance of disease-free status, whist maintaining shrimp in biosecure quarantine facilities before release into the environment.

• Conduct co-habitation trials of all imports with indigenous shrimp species to prevent the entry of unknown pathogens that pose high risks to local species.

Research and Development

• Fund programmes to investigate methods of combating disease threats (with public/private sector cooperation).

• Investigate advantages and disadvantages of exotic shrimp for the culture industry of each country to determine its suitability for import.

• Establish closed cycle breeding programmes to produce high quality SPF and SPR seed used for stocking ponds for both exotic and indigenous species.

• Identify all potential viral pathogens and develop specific and sensitive tools for their detection appropriate for both lab and farmer level.

• Research case-specific farming systems for each species so that it can be utilized optimally appropriate to local conditions.

• Establish programmes to monitor aquatic environments in and around shrimp farming areas, including effects of culturing new species on wild populations.

• Conduct routine analysis on the effects of new viruses on imported and indigenous hosts through cohabitation studies so that any effects or changes of viral pathogenicity can be monitored, and measures for its control investigated.

• Conduct routine monitoring of wild shrimp populations for all pathogenic viruses, including an assessment of which species develop the disease and which act as carriers, with attempts made to discover the source of any contamination.

• Assess the relative risk factors involved with each potential vector of shrimp pathogens to assist development of more appropriate intervention strategies for disease control.

• Evaluate viability of alternative shrimp farming systems (i.e. utilizing low-salinity and/or inland farming areas and high density, low impact culture systems).

• Investigate shrimp production and health management capabilities and practices to determine suitable codes and guidelines for culture of exotic species.

• Investigate best methods for dissemination of information pertaining to importation and management of exotic shrimp species.

• Develop epidemiological approaches to disease management.

• Evaluate water treatment methods for their ability to reduce disease risk.

• Develop simple, low-cost methods of reducing exposure to disease carriers.

• Evaluate the effectiveness of green water and shrimp/fish polyculture techniques for reducing disease outbreaks.

Infrastructure, Capacity building and Training

• Establish a network of collaborating and cross-referencing disease diagnosis laboratories with state of the art equipment and trained manpower.

• Consider reinvestment of export profits to improve health management capabilities.

• Develop biosecure high-health maturation systems and hatcheries for exotic and indigenous species with functional quarantine systems for holding imported animals whilst they are screened, and training facilities/extension for the local farmers.

• Develop a programme for the culture and genetic selection of exotic and indigenous species to aid development of improved broodstock with desirable culture characteristics, and training of farmers/extension agents in this technology.

• Allocate the necessary equipment, personnel, training and travel required for disease diagnosis, interpretation of test results, and assessment of shrimp health management practices at laboratory and farm level.

• Where required, provide overseas training or seminars from experts for government employees, trainers, extension officers and farmers on the techniques required to produce exotic species sustainably.

• Improve information dissemination and increase farmer awareness of issues involved with the importation and culture of exotic shrimp so that farmers have the facts and can clearly understand the potential risks and benefits involved. Collaboration between farmer's associations and the relevant government agencies would assist this process.

• Establish databanks on all shrimp farms, perhaps using GIS technology for effective regulation, assessment, monitoring and law enforcement.

• Promote training in the epidemiology of major shrimp diseases to improve awareness and develop practical health management schemes at farm, national and regional levels.

Industry Management and Technological Requirements

• A series of guidelines for health management in shrimp hatcheries and growout ponds were made at the Workshop on Management Strategies for Major Diseases in Shrimp Aquaculture in the Philippines in 1999 (WB/NACA/WWF/FAO, 2001).

• These were used as a basis for a subsequent Latin America/Asia inter-regional meeting on shrimp diseases funded by APEC, held in Mexico in 2000.

• Out of this meeting a report entitled “Technical Guidelines for the Management of Health and Maintenance of Biosecurity in White Shrimp Penaeus vannamei Hatcheries in Latin America” was produced (FAO, in press).

Industry based BMP recommendations

• The Global Aquaculture Alliance (GAA) has also produced and is distributing a set of “Codes of Practice for Responsible Shrimp Farming” and operating procedures for shrimp farming based on a 2001 survey of World shrimp farming practices.

• These guidelines were formulated to assist the development of national and regional codes of practice to help the shrimp farming industry and are available from the GAA website

• For example, the GAA Shrimp health management code of practice has, as its purpose, to promote shrimp health management as a holistic activity in which the focus is on disease prevention instead of disease treatment. They state that authorities on shrimp health management recognize that stress reduction through better handling, reasonable stocking densities, good nutrition, and optimal environmental conditions in ponds can prevent most infectious and non-infectious diseases.

• Also, treatment should be undertaken only when a specific disease has been diagnosed. In addition, effective measures must be taken to minimize the spread of diseases between farm stocks and from farm stocks to natural stocks.

References

Camera Nacional de Acuacultura (CNA) website: http://www.cna-ecuador.com

FAO 1995. FAO code of conduct for responsible fisheries. Rome, FAO. 1995. 41p.

FAO in press. Technical guidelines for the management of health and maintenance of biosecurity in white shrimp (Penaeus vannamei) hatcheries in Latin America. Part of the project: Assistance to Health Management of Shrimp Culture in Latin America: TCP/RLA/0071(A).

FAO/NACA 2000. Asia Regional Technical Guidelines on Health Management for the Responsible Movement of Live Aquatic Animals and the Beijing Consensus and Implementation Strategy. NACA, Bangkok and FAO, Rome.

Fegan, D., Arthur, J.R., Subasinghe, R.P., Reantaso, M.B., Alday de Graindorge, V. and Phillips, M.J. 2001. Consultant report: A review of trans-boundary aquatic animal pathogen introductions and transfers. In: Report of the Puerto Vallata Expert Consultation. APEC/FAO/NACA/SEMERNAP, 2001. pp. 132–175.

Global Aquaculture Alliance (GAA) website: http://www.gaalliance.org

ICES. 1995. ICES code of practice on the introduction and transfers of marine organisms 1994. Annex 3 of the report of the advisory committee on the marine environment, 1994. ICES Cooperative Research Report No. 204.

Lightner, D.V. et al. 2002. Six morphologically-distinguishable populations of P. stylirostris. Marine Biology 137 (5–6):875.

NACA/FAO 2001. Aquaculture in the Third Millennium. Subasinghe, R.P., Bueno, P.B., Phillips, M.J., Hough, C., McGladdery, S.E. and Arthur, J.R. (Eds). Technical Proceedings of the Conference on Aquaculture in the Third Millennium, Bangkok, Thailand, 20–25 February 2000. 471 pp. NACA, Bangkok and FAO, Rome.

OIE (Office International des Epizooties) website: http://www.oie.int

Rosenberry, B. 2002. World shrimp farming 2002. Shrimp News International, 276 pp.

SEAFDEC 2001. Regional guidelines for responsible fisheries in Southeast Asia. Responsible aquaculture. SEAFDEC, Iloilo, Philippines, 2001. 43pp.

WB/NACA/WWF/FAO 2001. Thematic Review on Management Strategies for Major Diseases in Shrimp Aquaculture. Proceedings of a workshop held in Cebu, Philippines on 28–30 November 1999. Edited by R. Subasinghe, R. Arthur, M.J. Phillips and M. Reantaso. 135 pp.

Wyban, J.A. and Sweeney, J.N. 1991. Intensive shrimp production technology. High Health Aquaculture Inc., Hawaii. 158 pp.

Role of exotic species in aquaculture: problems and prospects in Indochina

Amararatne Yakupitiyage
and Ram C. Bhujel

Abstract

National workshops were held in Cambodia, Lao People's Democratic Republic, Thailand and Viet Nam to consult local experts and users of introduced exotic aquatic organisms on the positive and negative impacts of the introduction, with a view to recommend the preparation of a regional code of conduct on the management of already introduced and new exotic species.

Exotic species have provided socio-economic benefits for a vast number of poor people in the region. There is no accurate information on their spread and negative ecological impacts as few studies have been conducted to evaluate these impacts. There is an urgent need to develop a well planned research program to assess the impacts. The governments should carefully weigh both the positive and negative impacts for each species before making any national or regional policy. After such evaluation it is necessary to develop a code of conduct for the management of alien species.

The code of conduct should address the issues of zoning, risk analysis, health certification, quarantine, development of inventory of species according to invasiveness and non-invasiveness, capacity building for monitoring and implementation of codes, and regional information exchange.

Introduction

Exotic animals are defined as “species occurring outside of its natural range”. Among numerous reasons for introduction of exotic aquatic animals into countries, aquaculture development is said to be a main motive (Welcomme, 1998 and FAO DIAS). Major concerns over the introduction of exotic fish are prolific breeding, predation or competition of the introduced species affecting indigenous biodiversity. These may lead to potential dominance of the introduced species, diseases transmission or contamination of local genetic pools.

There are two levels of aquatic animal introduction in Asia: (1) new species and (2) genetic variants or ‘strains’of a particular species. Review on potential impacts of exotic species in the Mekong Basin indicates that positive impacts far outweighed any negative to date. However, there is a need for developing Codes of Conduct to limit negative consequences of future introductions and regional guidelines for quarantine and health certification The Code of Conduct developed by European Inland Fisheries Advisory Commission (EIFAC) is usually taken as an example for such endeavours in Asia. Much of the recommendations made by various authors and organisations relate to present or future trans-boundary fish movements affecting genetic contamination and disease risk.

Many inland aquaculture species used in Asia are exotic. For example, with the exception of silver barb, striped catfish, and freshwater prawn, all cultured inland species in Thailand have been introduced within the last century. There are numerous unanswered questions regarding continuous use of exotic species in aquaculture such as:

• What are the existing guidelines for continuing the use of new and already introduced and established fish species in aquaculture?

• Have exotic fish established significant feral populations in Asia?

• Have they impacted adversely (ecologically as well as genetically) on local biodiversity?

• Have they introduced new diseases?

• What are the socio-economic benefits of these species?

• Does culturing these species benefit the rural poor?

• What is the trade-off between the environmental cost, if any, and the social benefits?

• Are there alternative indigenous species that can meet the needs of aquaculture production?

• What are the relative risks of spreading domesticated indigenous species on the genetic diversity of the same species within their natural range?

There is an urgent need to find answers to such questions. Environmental and poverty focused developmental organisations frequently question the ethics of using public funds for research and promotion of introduced exotic species.

The Asian Institute of Technology conducted National workshops in four countries: Cambodia, Lao People's Democratic Republic, Thailand and Viet Nam in search of answers to aforementioned questions. Key informants representing all stake holders were invited to gather and present information on impacts and to air national views on introduced species. The scope of this study was to examine the environmental and socio-economic impacts of the introduction of exotic species in South East Asia with focus on Thailand, Viet Nam, Lao People's Democratic Republic and Cambodia and consequently help develop a draft Code of Conduct and Regional Guidelines on the use of new and already introduced species in aquaculture in the region. This paper presents the major findings from the four national workshops as well as recommendations for developing Regional Guidelines to reduce/ eliminate potential negative impacts caused by exotic aquatic organisms.

National workshop methodology

Workshops were convened in Thailand (24 Sept. 2002), Cambodia (3 –4 Oct. 2002), Lao People's Democratic Republic (22–24 Nov 2002) and Viet Nam (20–21 May 2003); 30–40 key informants representing a wide range of expertise including fishermen, fish farmers, hatchery managers, extension workers, researchers, university lecturers, policy makers and environmentalists attended. Selected subject matter experts presented theme papers during the workshops. The participants were then divided into groups according to the profession e.g. producers, extension officers, academics and researchers. The major issues embodying the questions mentioned above were identified and discussed in the group sessions. Recommendations were then developed to alleviate negative impacts of exotic species introductions.

Current status on the introductions of aquatic organisms in Indochina.

A brief summary of aquatic animal introductions, their potential impacts, and the workshops' recommendations are presented below.

Cambodia

The participants identified 18 introduced aquatic species in Cambodia (Appendix A1) including, snails, crocodile and seaweeds. The purpose of introduction is said to be aquaculture development. Clarias gariepinus (African catfish) was the first fish species to be introduced from Viet Nam in 1982. Tilapia, silver carp, Indian carps (rohu, catla, mrigal) and common carp are found in natural water bodies in Kandal, Svey Rieng, Ta Kao, and Kampong Speu provinces. From the appearance in fishing lots, exotic species occupy less than 1% of the catch. Some of these species, e.g. Tilapia, Chinese and Indian carps, are said to be deliberately introduced by development projects or NGOs for aquaculture development. The rest of the species are believed to be either deliberately introduced or migrated by natural means from Viet Nam. No information about population size of exotic species in Cambodian waters is available, even though the first three species are widely used for aquaculture.

The participants identified following positive impacts of introduced species:

• easy to breed;

• small-scale farmers can produce seeds (seeds readily available);

• easy to culture (disease resistance, ability to use locally available feeds, and less attention to the culture system or less time spent for culturing fish);

• relatively higher production over indigenous species (faster growth and high survival);

• compatibility with agro-ecosystems (e.g. can integrated with rice farming or can grow in upland areas);

• source of alternative income (via sale of table fish or seeds);

• improves livelihood of people (poor people can either afford to buy exotic species due to relatively lower market price to culture them, improved nutrition of poor, improved income, employment opportunities);

• Golden snail has become a major protein source of animal/ fish feeds (poor people can collect 10–15 kg/day and sell to the feed companies).

Identified negative impacts were:

• over breeding of tilapia (cannot restrict to the culture system and escape to natural waters);

• water turbidity caused by common carp;

• potential negative environmental impacts;

• potential gene pool contamination (e.g. Clarias catfish);

• competition for habitats and natural food;

• potential loss of indigenous species (e.g. Notopterus notopterus is believed be decreasing in Angkor Borey district of Ta Kao province; some participant believe catch (including Notepterus) has been reduced by 20% after introduction of tilapia or other exotic species);

• potential for disease contaminations;

• low demand (low price);

• potential price drop of indigenous species due to cheaper price of introduced species;

• Golden snail damages rice paddy.

The Cambodian workshop recommended that:

• Cambodia should not import new exotic species;

• only indigenous species should be used in fish releasing ceremonies;

• hatchery and culture technologies for indigenous species should be developed;

• research should be conducted to evaluate the impacts of existing exotic species;

• the country should promote culture of exotic species away from natural water bodies;

• the Ministry of Agriculture should develop guidelines/ regulations for movement of existing/new exotic species within country;

• the regulation should delineate zones that exotic species can be cultured (rural areas away from natural waters).

Lao People's Democratic Republic

Exotic species introduction has long history in Lao People's Democratic Republic. However, as fish culture is new to Lao People's Democratic Republic, most introductions (Catla, Mrigal, Rohu and common carp) were brought in 1977 from India and Thailand for aquaculture development with the assistance of international organizations. Nile tilapia was introduced from Thailand in 1965. Clarias gariepinus was introduced from Viet Nam in 1980 for aquaculture development. Participants of the workshop pointed out that there are about 13 alien species introduced. (Appendix A2). However, only common carp and Nile tilapia have established their population in the wild through natural reproduction.

Except for the golden apple snail, no information is available on the negative impacts of introduced species. Nile tilapia and common carp are used for cage culture. In 1995, farmers accidentally have released cage cultured fish to Nam Ngum reservoir. Participants claimed that after this incidence, there was an increase in Nile tilapia, bighead carp and common carp population in the reservoir. The participants identified that grass carp, common carp and African catfish as high risk species

The workshop recommended that:

• introduction of new exotic species should be strictly controlled and exotics already introduced should only be used for pond culture;

• high risk species such as grass carp, common carp and African catfish should not stock in the natural water bodies;

• enhance public awareness on potential negative impacts of these species

• should develop proper quarantine procedures;

• conduct research to evaluate negative impacts pf already introduced exotic species and socio-economic benefits of using native and less risk exotic species;

• develop culture techniques for indigenous species;

• should develop appropriate policies, management tools taking both positive and negative impacts into account;

• develop specific measurement for developing zones that allowed to culture exotic species and to control fish movement;

• strengthen the manpower and build the capacity for implementing policies and regulations.

Viet Nam

Participants of the workshop agreed that there have been uncontrolled introductions of 30alien species in Viet Nam (Appendix A3). Chinese carps were introduced directly from China in 1958 by the Government of Viet Nam. Indian Major Carps were introduced from Lao People's Democratic Republic in 1984 with the help of an international organization. All these Indian and Chinese major carps are still widely used for aquaculture and have also established their population in the wild. Oreochromis mossambicus was brought from Africa and the Philippines by the private sector for farming in 1951 and 1955 respectively. It has established its population in the wild through its prolific reproductive nature. It is also widely cultured. Nile tilapia was imported from Taiwan, Philippines and Thailand. Pomacea canaliculata has been found in Viet Nam in 1988 and has most probably been introduced through the ornamental fish trade.

Alien aquatic animals are introduced to Viet Nam to diversify fish production, improve genetic materials and reduce inbreeding, improve food security, improve farmer income, creating job opportunities, use for ornamental purposes, and to use as larval/ aquarium feed e.g. Artemia. These introduced species are preferred by farmers due to well developed breeding and culture technologies, breeding potential in captivity (e.g. P. vannamai), high fecundity, resistance to certain diseases, higher production (fast growth and high survival), higher dress weight, ability tolerate adverse water quality, and the commercial value in both local and export markets.

The participants identified following benefits of introduced species:

• enhanced aquaculture production (fast growth, high survival rate, high dress weight);

• high market value;

• foreign exchange earning;

• enhanced food security of poor e.g. 35% exotic species production is used for local consumption, mainly by the poor;

• improvement in farmer income and employment opportunities;

• offer opportunity to develop hybrids that have higher growth compared to the local fish e.g. common carp and mechanism to resolve inbreeding problem of introduced species;

• can use for waste recycling/ local resources, weed control e.g. grass carp, and for mosquito control;

• some species do not breed/ survive in the natural environment e.g. introduced Artemia;

• use as live food e.g. Artemia;

• provide opportunity for in-country broodstock development;

• easy to enhance stocks;

• aesthetic and social (status) value of some ornamental species.

Since no studies have been conducted on ecological or genetic impacts, there is no scientific evidence for negative impacts. The only species that has shown clear negative impacts is the golden snail destroying rice fields. Other species that have potential for negative impacts are tilapia, grass carp, silver carp, bighead carp, Colosoma, P. vannamei and sucker catfish as they have established significant feral population in the natural environment. Gene pool contamination is common in some species e.g. between native and Chinese silver carp hybridization, and common carp (native and imported). Inbreeding problems of exotic species are common, e.g. African catfish originated from only one pair of fish.

Exotic species have introduced new parasites and diseases e.g. three new species of monogenea come with tilapia, and have reduced biodiversity by changing the species composition natural water bodies e.g. fishers in Thac Mo Reservoir in Binh Phuoc province believed that tilapia has eliminated or reduced some local fish species in the lake.

Import of exotic species is controlled by restricting species that can be imported e.g. there is a list of aquatic species which can be imported to Viet Nam. The Natural resources protection act, 1989, provides guidelines for methods of protection of indigenous aquatic resources. Decision paper, 2002, shows procedures to import new species i.e. should be disease free, for experiments, and how to receive permission to release to natural environment

The Vietnamese workshop recommended that:

• research should be conducted to evaluate positive/negative impacts;

• methods for environmental impact assessment of exotic fish species should be developed;

• strict implementation of aquatic animal inspection procedures by the custom department;

• proper quarantine system should be developed;

• control mechanisms for controlling invasive exotic species such as golden snail should be developed;

• regulation for the stocking of fish species to natural water bodies should be developed;

• trans-boundary animal movement regulations should be developed and implemented;

• code of conduct for exotic species (import and their use) should be developed;

• capacity to implement regulations (the development of manpower) should be strengthened.

Thailand

Altogether 163 aquatic organisms including seven species of frogs, seven crocodile species, three shrimp species, over 100 species of ornamental aquatic organisms and about 20 food fishes (Appendix A4) for the aquaculture development have been introduced into Thailand during the last century. Nile tilapia (Oreochromis niloticus) was introduced as a gift by the Crown Prince of Japan to the HM King of Thailand in 1965 (Pullin, 1988) then distributed to the farmers through department of fisheries after successful breeding, which has been widely used for aquaculture. This species is now widely distributed in the natural ecosystem. There is some evidence that tilapia has become a main species in Ubolratana (up to 40% catch) and Lam Ta Kong reservoirs, but no information on negative impacts are available. Although other tilapia species such as T. rendalli, T. zilli, O. aureus and O. mossambicus were also introduced into Thailand, they were not cultured. Red tilapia is found in the country but they are not separate species and thought to be the hybrids of O. niloticus and O. mossambicus. Recently, new red tilapia hybrids have been introduced from various countries e.g. Taiwan, Virgin Island, Scotland, and Malaysia. This hybrid has become commercially important species to Thailand as it has higher demand due to their attractive colour. Salinity tolerance and faster growth have made red tilapia popular in coastal areas.

A few alien species have established their populations in the natural environment through natural reproduction. Out of over 30 exotic food fish species, only carps, tilapia, hybrid catfish and white shrimp have been commercially used for aquaculture. Populations of grass and silver carps have been established through continuous re-stocking into the lakes and reservoirs for their characteristic feature of controlling excessive vegetation and plankton bloom respectively. An exotic sucker fish has been found in the rivers of Thailand which has been caught by fishermen in large numbers.

Increased freshwater fish production, provision of protein source to rural poor, income and employment generation and enhanced export income are the major positive benefits of introduced food fish species (Boonchuwong, 2002). A fish consumption survey in 1998–1999 in seven provinces of North, Northeast and central regions has shown that Thai people on average consumed 28.8 kg fish/person/year. Exotic species accounted for 12kg fish/person/year (41.6%) of the total fish consumption. The highest consumed exotic species is Nile tilapia which account for 8.52 kg fish/person/year for the seven provinces. Nearly 46% (13.8kg fish/person/year) of fish consumed in rural areas are exotic species (Boonchuwong, 2002). Nile tilapia accounts for 9.84 kg fish/person/year (33%) of the total fish consumption (29.88 kg fish/person/year) in the rural areas of the seven province.

Table 1. Aquaculture production including marine species (FAO 1999, 2001)

Very limited research has been conducted in Thailand to evaluate the negative impacts of fish introductions. Na-Nakorn et al. (2002) showed evidence for presumed genetic introgression of Clarias gariepinus genes into indigenous C. macrocephalus and called for making proper management plans for protecting aquatic biodiversity. They also uncovered genetic differentiation between hatchery bred stock of silver barb (Puntius gonionotus) and their wild counterparts and cautioned that restocking programs should not use aquaculture stocks.

National laws prohibit introduction of well known invasive fish species e.g. piranha and twelve other endangered aquatic organisms. Other control measures are restricted to avoid disease outbreaks and dangers to the consumers. Other species can be imported to Thailand taking permission from competent officials. However, the main problem of controlling the introduction of exotic species is lack of proper regulation and implementation (Chinabut, 2002).

Thai national workshop recommended:

• conduct new research to evaluate ecological and socio-economic impacts,

• develop culture technologies for indigenous species,

• develop procedures for risk assessment studies,

• risk assessment studies should be conducted before allowing the introduction of new species,

• implement existing guidelines and assign a group to oversee introduction of exotic species,

• develop guidelines and manuals for each alien species and analyse the risks.

Conclusion and recommendations

A vast number of exotic species has been introduced to SE Asia. Some introduced species (e.g. tilapia, common carp) have established significant feral populations and the local communities consider them indigenous species. There is some evidence on the alteration in genetic make-up of the indigenous species (e.g. Clarias sp. in Thailand), and in the catch composition (e.g. 70–80% catch from Cheng Ek lake in Phnom Penh said to be tilapia).

Exotic species have made socio-economic benefits to each country covered in this study. The exotic species have played significant roles in ensuring food security. These species accounted for about 49, 100, 26 and 73% of the total aquaculture production in Cambodia, Lao People's Democratic Republic, Thailand and Viet Nam, respectively (Table 1).

Since the culture technologies are well developed for these species, they have served as gateways of knowledge and skills for aquaculture development in the region. Hatchery and culture operation, and research into exotic species have given a large number of employment opportunities. Exotic species have served as agents for crop diversification for rural poor.

According to Dowall (1996), introduced Nile tilapia and common carp maximized the natural fertility of the paddy fields in Cambodia. Introduced trout has been reported to increase benthic phosphorous availability and stimulate the primary production (Schindler et al., 2001).

There are a number of negative impacts have been attributed to exotic species. The population of Notopterus notopterus has been reported to be declining in Cambodia (especially in Ta Kaew) and other fish also have been reported to be declining due to exotic species such as tilapia which constitutes up to 80% of the catch in Chiang Ek Lake near Phnom Penh. In Lao People's Democratic Republic, it has been suspected that the native prawn has declined. Hamparadispa sp. and Pla Ka in Nam Ngum reservoir in Lao People's Democratic Republic and a local snail have disappeared most probably due to exotic fish introductions. Tilapia has also been found abundantly in the wild of all four countries studied here. In Ubonrat reservoir, tilapia can constitute up to 40% of the catch. Tilapias have also been caught in large volumes in other reservoirs of Thailand. De Iongh and Van Zon (1993) studied the impacts of the introduction of common carp, Nile tilapia, and Indian and Chinese carps into the lakes and reservoirs in northeast Thailand. According to local fishermen who caught sucker fish in large numbers from the rivers of Thailand the species might have serious impacts on indigenous species as it is a carnivorous. Participants agreed that the sucker catfish (Hypostomus plecostomus) has been seen in significant numbers in the natural water bodies in all the four countries, especially in the rivers.

Several diseases and parasites have been diagnosed in the exotic fish species in each of the four countries. However, it is not clear whether all these disease pathogens came with the imported fish or not. In Thailand, three fish diseases have been recorded as having entered the country along with the introduced fish (Piyakarnchana, 1989). One of the most devastating examples is white spot disease that causes virus in shrimp which was suspected to be transmitted through importation of shrimp larvae, adults, even through frozen forms and other modes (Jory et al., 1999; Soto et al., 2001).

There are many alternative indigenous species in the region as the Mekong River and its tributaries are rich in natural flora and fauna. There are over 1000 indigenous species identified. However, very limited studyies have been done so far in order to bring them into culture. Silver barb has been an important species among the cyprinids. Some studies are under way on the breeding and culture of seven Mekong indigenous species. There are indications that they can be bred and cultured in captivity but are much difficult to breed and grow slower than exotic species.

Exotic species have created socio-economic benefits for a vast number of poor people in the region. More information is needed on their spread and impacts (Welcomme and Vidthayanon, 2000) There is an urgent need to develop a well planned research program to assess the impacts. The governments should carefully weigh both the positive and negative impacts for each species before making any national or regional policies. After evaluating positive and negative effects, it is necessary to develop guide lines for management of alien species.

The participants of four national workshops recommended that the countries should be cautious of future introductions of new exotic species and their release into natural water bodies. Although there are some existing regulations in these countries, there are no specific laws or implementing agencies. All four countries suggested efforts should be made to develop common agreement of regional level cooperation.

Although there are many international conventions and agreements to address the issue e.g. for example, FAO Code of Conduct for Responsible Fisheries, ICES/IFAC code, Convention on Biological Diversity (CBD), WTO agreements of Animal health and certification, OIE aquatic animal health, Bio-safety regulations, Ramsar Convention, FAO/NACA fish health guidelines, French Rural Code, none of them adequately and appropriately addresses the issue of introductions and regulations of exotic species in the region. Therefore, participants recommended developing a suitable code of conduct taking cultural and economic situation into account. The code of conduct should also address the issues of zoning, risk analysis, health certification, quarantine, development of inventory of species according to invasiveness and non invasiveness, capacity building for monitoring and implementation of codes, and regional information exchange.

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Appendix A1

Some important exotic species identified by the workshop participants in Cambodia

Appendix A2

Major exotic species and their impacts identified the workshop participants in Lao People's Democratic Republic

Appendix A3

Major exotic fish/shrimp species introduced to Viet Nam identified by the workshop participants

Appendix A4

Major exotic freshwater fish/shrimp species identified by the workshop participants in Thailand