Increasing concern over the effects of previous transboundary movements of pathogens has led to the establishment of codes and guidelines for health management and movement of live aquatic organisms. Such codes and guidelines, developed by various global and regional organizations (ICES, OIE, FAO, etc.), have been in place for some time, whilst new agreements specific to Asia-Pacific, although voluntary, have been also established recently by FAO, NACA, SEAFDEC and ASEAN (as described in Section 7.1). Despite their official adoption and the establishment of national legislation and regulatory frameworks (to varying degrees) by several Asian countries involved, they have so far failed to prevent repeated transboundary movement of P. vannamei and P. stylirostris and in many cases their attendant serious viral pathogens.
The restrictions placed by various governments of the Asia and the Pacific are discussed in Section 7.2. Very few Asian countries have so far managed to completely prevent the introduction of P. vannamei (i.e. Sri Lanka). Most have allowed importation of some, supposedly disease free PL or broodstock, under government supervision (in many cases without adequate facilities to verify quality and without conducting proper risk assessments). However, in nearly every case, the difficulty or expense involved with such introductions, combined with the impatience of shrimp farmers (who have seen declining revenues due to the effects of previously introduced viral pathogens) have circumvented the official process and illegally brought in cheaper animals which are not certified disease free. Such a scenario has been seen in Thailand, Indonesia, the Philippines, India, Viet Nam and Malaysia, all within the last two to five years. In the cases of Thailand and Indonesia, and probably the other countries (although this remains to be confirmed), such movements have already led to the introduction of at least one notifiable and serious pathogen of cultured and wild shrimp, the Taura Syndrome Virus (TSV). There are also suspicions that other viral pathogens have been introduced along with the P. vannamei, which may have led to problems with the primary indigenous cultured shrimp species P. monodon (i.e. LOVV in Thailand).
There exist many reasons for the ineffectiveness of these restrictions, which have allowed the illegal importation of PL and broodstock animals that have not originated from disease free facilities (as stipulated in the codes), in most cases by the private sector. Most problems have involved the predominance of producers in driving such imports due to the perceived benefits of the introduced species. The possible reasons are detailed in Section 7.3.
Nonetheless, in the short term at least, significant industries based upon the introduction and culture of P. vannamei into these countries, and P. stylirostris into Brunei, have developed. The culture of these alien species is beginning to replace the culture of indigenous species which have suffered chronic disease problems, leading to declining production throughout Asia during the past decade. Ironically, it appears possible that at least some of the problems encountered with the indigenous species may have resulted from viruses imported with their alien shrimp hosts.
The only Asian countries not to have placed limitations on the importation of P. vannamei from any source were Mainland China and Taiwan Province of China, who have imported this species in great quantities (initially) over the past eight years. This resulted in the simultaneous introduction of TSV and other viral pathogens. Although TSV is currently causing serious mortalities in cultured P. vannamei in these countries, it has not yet been proven to result in problems for other shrimp species. Neither has it prevented the massive expansion of P. vannamei farming in these countries, such that it has now reached 300 000 metric tonnes (71 percent of estimated total shrimp production in 2003) in Mainland China and 8 000 metric tonnes (42 percent of estimated total shrimp production in 2002) in Taiwan Province of China. However, the successful development of the culture industry for P. vannamei in China has led to the export of non disease-free stocks, which appear to have contaminated other Asian countries with pathogenic viruses.
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 associated viruses, will remain in most countries.
A more pragmatic approach might 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 for this could be strengthened, since it has been the inability to effectively control imports which has allowed the introductions to date.
This approach at least offers a working solution to the reality that P. vannamei is already present in many countries and being cultured at significant economic levels in several. This also allows countries to take advantage of the potential benefits offered with this alien 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 current conditions in Asia.
Some North and Latin American countries have shown that even with the introduction of the alien P. vannamei, it is possible to limit the introduction of viral pathogens and develop sustainable industries. Examples of this have been seen (despite initial mistakes) in Hawaii and the USA, which have managed to eradicate WSSV from their culture industries, however, the subsequent re-entry or re-emergence of the disease in Hawaii underlines the importance of continued monitoring and surveillance. Similarly, the creditable efforts of Brazil and Venezuela, who have initially prevented the introduction of WSSV and have growing industries for P. vannamei, are also threatened by irresponsible movements.
These successes were facilitated by some of the properties of P. vannamei (shared by P. stylirostris) that provide them with the potential to be introduced to new countries/regions and generate successful industries, without the problems of simultaneously introducing new pathogens. These properties are associated with the fact that the life cycle of these species has been closed and (partially) domesticated strains of genetically selected, fast growing, disease free (SPF) and disease resistant (SPR) animals are commercially available. These properties are not shared by P. monodon, the leading cultured shrimp of Asia (although work is in progress), but are common to the vast majority of animals cultured by humans today.
It was through the use of these lines and the strict application of the codes of conduct and health management strategies mentioned above that the American countries were able to successfully introduce these alien species without negative biological consequences. Conversely, it was through the disregard of these principles that the negative aspects of introducing P. vannamei to Asia were able to proliferate. Clearly, it is possible to minimize the risks associated with transboundary introductions of these species and the following recommendations are made in that regard.
The broader ecological impacts of the introduction of alien shrimp species such as P. vannamei and P. stylirostris has been neither well studied nor well documented in the Asia-Pacific. Perceived risks and potential impacts remain unresolved and any country considering the introduction of these alien species should certainly conduct comprehensive risk analysis and assessment, including environmental, social, and economical risks involved with such movements.
This review examines the history of introductions of alien Penaeid shrimp species to the Asia-Pacific region and current knowledge of the social, economic and environmental impacts of these introductions. Present information on impacts is currently very much focused on disease problems, reflecting the major concern of the shrimp industry. An understanding of the impacts on aquatic biodiversity, and indeed the social and economic costs and benefits over anything much beyond the duration of a crop cycle from these alien shrimp introductions, is much more limited. Nevertheless, there are clearly a number of lessons that can be learned from the present situation and recommendations that can made from present experiences. These span advice to both governments and the private sector in countries where these alien species have not been introduced, or where there have been limited introductions to date.
These recommendations also draw on other recent publications regarding the health implications of the importation and sustainable culture of alien shrimp species (and their attendant pathogens), particularly 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 focus is on the issues involved with the transboundary introduction and management of P. vannamei and P. stylirostris in Asia.
- importing shrimp only from facilities with demonstrated disease absence. This would require that shrimp exports have a minimum two year disease-free status, are certified as such and can submit independent, qualified certification of their status;
- restrict severely the import of shrimp coming from uncertified sources of shrimp;
- 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 cohabitation trials of all imports with indigenous shrimp species to prevent the entry of unknown pathogens that pose high risks to local species;
- develop biosecure high-health maturation systems and hatcheries for alien shrimp species with functional quarantine systems for holding imported animals whilst they are screened, and training facilities/extension for the local farmers; and
- develop a programme for the culture and genetic selection of alien and indigenous species to aid development of improved broodstock with desirable culture characteristics, and training of farmers/extension agents in this technology.
- A series of guidelines and recommendations 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). The principal recommendations of this workshop are presented in Annex I.
- The recent FAO publication Health Management and Biosecurity Maintenance in White Shrimp (Penaeus vannamei) Hatcheries in Latin America (FAO, 2003) provides information on how to improve the health and quality of P. vannamei postlarve produced in hatcheries in Latin America through improved facility maintenance and husbandry, broodstock maturation, larval rearing, feeding, water quality management, biosecurity, and health management, using interventions at different points of the hatchery production process.
- The document also provides valuable information on how Hazard Analysis Critical Control Points (HACCP) type interventions could be applied during hatchery production of P. vannamei postlarvae. The information provided in this document will contribute to the efforts by the P. vannamei hatchery operators and mangers in producing quality, disease-free, healthy post larvae, thus improving overall production and sustainability of white shrimp aquaculture.
- The major protocols detailed in the FAO (2003) document are given in Annexes II and III.