- Email: [email protected]
Biosecurity: application in aquaculture
Aquacultural Engineering 32 (2004) 3–10
Biosecurity: application in aquaculture Gary D. Pruder∗ The Oceanic Institute, 41-202 Kalanianaole Highway, Suite 9, Waimanalo, HI 96795 USA
Abstract The introduction and discussion of biosecurity in aquaculture occurred in 1997 in a World Aquaculture Society (WAS) Special Session titled, ‘Sustainable Shrimp Farming: Emerging Technologies and Products for Biosecurity and Zero Discharge.’ By 2003, proceedings of several workshops were published which offer very valuable information on the need, application and problems with biosecurity. These published proceedings are identified and discussed. While biosecurity is relatively new to aquaculture, other agricultural animal production systems, namely poultry, have fully developed and finely tuned biosecurity procedures in place. The adoption of biosecurity protocols in shrimp aquaculture has required significant changes in the shrimp stocks and adjustments in feeds and feeding, genetic traits for selection, and overall production procedures. Biosecurity in aquaculture is a maturing activity, still in need of improved information on diagnostics, disease transmission, clean up and eradication. Biosecurity, health, nutrition genetics and environmental quality must be integrated to achieve a uniform and low cost product on demand. © 2004 Elsevier B.V. All rights reserved. Keywords: Poultry; Shrimp; SPF; Water Exchange; Feed Nutrition; Microbes
1. Introduction The invitation from Dr. Tony Schurr to present a paper on Biosecurity in Aquaculture was directed to the Oceanic Institute (OI). Having been involved in the intricacies of recognizing the need for and initiating initial applications of biosecurity in marine shrimp culture and knowing that the audience would be largely engineers, I personally accepted the invitation. The preparation of this manuscript led me to three principal references which together summarize biosecurity applications in aquaculture and events leading up to the ∗
Corresponding author. Tel.: +1 808 259 3102; fax: +1 808 259 5971. E-mail address: [email protected] (G.D. Pruder).
0144-8609/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaeng.2004.05.002
4
G.D. Pruder / Aquacultural Engineering 32 (2004) 3–10
need for biosecurity in marine shrimp farming. The references are listed below with a brief description of their content and contributors. The special session was conceived and planned at a time when the shrimp industry worldwide was suffering severe mortality problems related to diseases (Browdy, C.L. and Hopkins, J.S., 1995 (Editors)). Twenty-two scientists worldwide, selected for their expertise across the whole range of sustainability problems, were invited to prepare and present manuscripts. Each of the authors made significant contribution of time and expertise. The results of their dedication provide a valuable compendium of some of the best and latest information on shrimp farming for researchers, and producers addressing recent sustainability problems. For a number of years, investigators dedicated to the development of advanced shrimp farming technologies have drawn comparison, with agricultural animal husbandry industries (Bullis, R.A. and Pruder, G.D., 2000 (Editors)). Principal comparisons have centered on the integration of genetically-improved, high-health stocks, advanced feeds and feeding methods and disease control and biosecurity. The planners and organizers of the special session offered direct comparisons by alternating presentations by chickens and shrimp experts, followed by a round table discussion. Of the ten papers, four were by industry and university chicken experts, the remaining six were by research scientists of the U.S. Marine Shrimp Farming Consortium. This workshop was organized by the Aquaculture Exchange Program of OI and funded by the Department of Commerce (Lee, C.-S. and O’Bryen, P.J., 2003 (Editors)). Scientists worldwide were identified and invited to participate based upon their expertise in biosecurity measures used against the spread of bacterial disease, viral diseases and parasites in production systems for major aquaculture species. The workshop was organized to allow information exchange regarding regulations and management practices in preventing disease outbreaks in finfish, crustaceans and mollusks. Sixteen papers and a summary discussion are included in the publications. Discussions focused on biosecurity basics, type of diseases that should be addressed through biosecurity, detecting and eliminating disease transmission, non-fish disease vectors and the effectiveness of regulatory enforcement. The quality of this information should be instructive for those wishing a sound understanding of principles, practices and weaknesses of current efforts in aquaculture. Therefore, this manuscript will highlight various aspects and attempt to show that, while biosecurity is a vital activity, it is one of several vital activities that are interactive and interdependent. These other activities are genetics, nutrition, health and improved production systems. The poultry industry is used as a cornerstone or point of departure for application of biosecurity in aquaculture. Perhaps more than any other segment of animal agriculture poultry has relied on technological innovations made possible through scientific discovery. Poultry remains a viable model for aquacultural development. It is noted that the poultry model extends beyond science and technology. Although not a core subject, this manuscript highlights various marketing, product forms (over 3,000) and product differentiation are crucial aspects whose effect may have exceeded technology in underpinning the world competitiveness of the poultry industry. A successful aquaculture industry in the United States cannot be built solely on technology.
G.D. Pruder / Aquacultural Engineering 32 (2004) 3–10
5
2. Biosecurity Guillermo Zavala (2000) defined biosecurity in the poultry as an essential group of tools for the prevention, control and eradication of economically important infectious diseases in poultry. Biosecurity in aquaculture has been defined as the sum of all procedures in place to protect living organisms from contracting, carrying, and spreading diseases and other non-desirable health conditions (Moss et al., 1998). As applied to aquaculture, the scope of biosecurity has yet to be adequately defined but its activities will be comprised of preventive medicine, adequate diagnosis, contain outbreaks that occur, disinfection and eradication. Biosecurity is a shared responsibility, in that each individual in the process of animal production plays a different but critical role in the implementation of an overall program. Any failure in the chain of process will undercut the overall effort to establish and maintain biosecurity. In general, biosecure operations should have a defined structure and barriers, such as fences and gates in place. The faculty should be constructed with materials that can be disinfected easily should a disease outbreak occur and is free from unauthorized access such as vehicles or people. Structurally, it should also prevent the escape of target animals and the entry of other animals. It should be sited away from hazards that are potential sources of infection or contamination. Untreated surface water should not be used as the source water because it may contain pathogens. The ideal system should have appropriate back-up water, life support systems and operational procedures that allow one-way flow, so that nothing can be returned to the facility without disease screening. Biosecurity is practiced at three intensity levels: (1) specific pathogen-free (free of defined infectious agents) for vaccine and laboratory reagent production (2) primary breeding industry, (3) commercial grower level. In general terms the resources for disease control involve one or more of the following aspects—quarantine; control traffic of personnel, vehicles and equipment; vaccination and/or medication; diagnostic testing; depopulations and eradication.
3. The poultry case In 1948, it took 94 days to grow a four pound chicken and the feed conversion ratio was 3.85/1. Today the same weight chicken takes 38 days with a feed conversion of 1.80. In other words, today’s chicken grows more than twice as fast on less than half the feed. These resulted through an integration of health, biosecurity, improved production systems, nutrition and genetics. Without biosecurity this revolution could not have occurred. The half century of innovation in poultry productions is an excellent example and perhaps a model for aquaculture. Samuel L. Pardue (2000) provided an instructive review, from which the following extracts are highlighted. ‘Within the past half century, a barnyard enterprise has evolved into a dynamic global poultry industry. Through the adoption of management philosophy that embraces technology, the poultry industry has witnessed advances in efficiency and uniformity of production that are unparalleled.’
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G.D. Pruder / Aquacultural Engineering 32 (2004) 3–10
The United States alone produced nearly a quarter of the 51 M mt of chicken produced around the world. There were major forces that contributed to the development of the poultry industry including expansion, consolidation, integration, scale, marketing, product differentiation, overall automation, and scientific discovery. Repeating a point made in the introduction. However, for the purposes of this paper on biosecurity, this manuscript concentrates only on scientific discovery. Two major disciplines, genetics and nutrition, have had a mutually beneficial relationship with poultry for much of this century. ‘Several characteristics have contributed including relatively short generation time, small body mass, low cost of maintenance and a non-ruminant digestive system. Understanding of the nutritional requirements of the chick probably exceeds that of all other animals including humans. Bruce Glick’s discovery of bursal-derived lymphocytes (B cells) in the chicken revolutionized our understanding of humoral immunity Glick et al. (1956). The poultry industry is most advanced in the understanding and exploitation of immunosuppressive diseases.’ Vaccines, thus, play a cornerstone role in modern poultry production. However, the largest single contributor to advances in poultry production is selective breeding supported by nutrition, management and health activities. Milton L. Boyle III, stated that, “the similarities between the genetics of poultry and shrimp are striking and include economic traits of interest as well as their heritabilities and genetic interactions. Poultry breeding involves intense and sophisticated selection schemes, even to the point of niche marketing and multiproduct development. Biosecurity is vital and exists at a stringent level at the breeding facilities, where disease outbreaks would be catastrophic.” Importantly, very early chicken breeding efforts initially targeted growth rates and disease resistance. ‘Broiler commercial traits now include growth rate, feed efficiency, meat yield, body conformation, livability, skeletal integrity and feathering. Reproductive traits include hatching egg production, age at first egg, egg size, egg shape, breeder livability, fertility, and hatchability. In many cases the traits are antagonistic to each other so that balanced breeding schemes are utilized.’ Specific efforts to breed for disease resistance resulted in much slower growing chickens. The advent of vaccines and the development and exploitation biosecurity protocols replaced the much costlier and unreliable genetic selection for disease resistance. ‘Decades of research in poultry diseases have rendered invaluable information that is now used by the poultry industry on a daily basis. Many microorganisms have been well characterized in their pathogenesis, even to the molecular level. This was essential for the development of vaccines and diagnostic tools. Without the research and understanding of such poultry pathogens it would have been impossible to control them. The parallel between the poultry industry a generation ago and aquaculture are more than apparent. Whether aquaculture can utilize the poultry model remains to be seen. The poultry model does, however, raise intriguing questions as to the future of this growing aquaculture agri-business.’ 4. The marine shrimp case 4.1. Specific pathogen-free (SPF) shrimp In the 1990s shrimp farms around the world were experiencing severe economic losses due to low yields and high mortalities. The problems cut across national boundaries, species,
G.D. Pruder / Aquacultural Engineering 32 (2004) 3–10
7
culture system and environmental conditions. The principal disease vector appeared to be diseased or disease carrying shrimp seed, both wild and hatchery-reared. Farms in the United States that were using high-health shrimp provided by OI as part of the U.S. Marine Shrimp Farming Consortium (USMSFC), were seemingly unaffected. However, the import of foreign produced shrimp seed to both South Carolina and Texas resulted in severe crop loss. The point had been made that bringing diseased or disease carrying shrimp onto farms was an invitation to disaster. In 1993, Wyban et al. differentiated between high-health and specific pathogen-free broodstock and seed, commonly used terms that are poorly understood and often misused. It was explained that reference to high-health stock, rather than SPF, reflects a loss of control over the health status of the stock. In this paper, SPF stocks relate only to stocks retained in the breeding center that have already undergone rigorous quarantine and screening efforts. Once stocks leave the breeding center, they are considered high-health, which means they are free of certain pathogens to the best of our ability and understanding. The process of establishing SPF stocks is shown (Fig. 1) and the list of specific pathogens is also shown (Table 1). The cornerstone of the emerging genetic improvement program is SPF stock gathered from around the world. Genetic research on shrimp indicates that their heritability estimates for commercially important traits are similar to poultry. This indicates the potential for genetic advance in shrimp is formidable. Rapid progress is being made in breeding shrimp for very high growth rates at very high densities.
Fig. 1. Development of SPF shrimp.
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G.D. Pruder / Aquacultural Engineering 32 (2004) 3–10
Table 1 Working list of specific pathogens for SPF shrimp Pathogen type
Pathogen/pathogen group
Pathogen category
TSV–picornavirus WSSV–nimavirus (new family) YHV/GAV/LOV3 –roniviruses (new family) IHHNV–systemic parvovirus BP–occluded enteric baculovirus MBV–occluded enteric baculovirus BMN–nonoccluded enteric baculovirus HPV–enteric parvoviruses
C-1 C-1 C-1 C-2 C-2 C-2 C-2 C-2
NHP–alpha proteobacteria
C-2
Microsporidians Haplosporidians Gregarines
C-2 C-2 C-3
Viruses
Procaryote Protozoa
Pathogen category with C-1 pathogens defined as excludable pathogens that can potentially cause catastrophic losses in one or more American penaeid species; C-2 pathogens cause economically significant disease and are excludable; and C-3 pathogens cause less serious disease, but should be excluded from breeding centers, hatcheries, and some types of farms.
Although vaccines, medicated feeds, and immunostimulants are effective in combating some pathogens in other meat-producing industries, they are either unavailable to shrimp farmers or their efficacy is unproven. Various strategies are being employed to mitigate the risk of disease including, high-health seed, reduced water exchange rates and screening influent water. Genetic selection can enhance disease resistance in farmed plants and animals, including fish (Gjedrem et al., 1991). However, the heritability estimate for disease resistance in white shrimp was 0.09 ± 0.03. Tave (1993) reported that heritability estimates less than 0.15 are difficult to improve by selection. Nonetheless, OI was able to increase resistance to Taura syndrome virus (TSV) in a few generations. However, note that subsequently TSV now occurs as TSV 1, TSV 2, and TSV 3, due to natural phenomenon for which the selected shrimp have less resistance. In light of the limitations in breeding for disease resistance, selective breeding should not be perceived as a panacea to the health problems plaguing the shrimp industry. In the absence of vaccines and effective selection for disease resistance, the shrimp industry has two principal opportunities to control disease—high-health stocks and biosecurity. 4.2. Zero-water exchange The second most likely source of disease and/or disease causing organism is water exchange. The using of raw or untreated make up water is responsible for continued disease problems when ponds are stocked with high-health shrimp seed. Fill and exchange water needs to be disinfected. The cost of water disinfection quickly drove production system research under the zero-water exchange banner. Biosecure shrimp production systems stocked
G.D. Pruder / Aquacultural Engineering 32 (2004) 3–10
9
Fig. 2. Growout and system management.
with high-health seed represent an emerging technology with an environmentally sustainable and economically viable alternative to conventional shrimp culture. Such systems have been described previously (Moss, 2002; Browdy and Bratvold, 1998; Pruder et al., 1995; Wyban et al., 1993). 4.3. Feed, nutrition and microbes The restricted use of water exchange rippled through shrimp growout technologies causing major changes in feeds and feeding and the maintenance of mixed microbial populations. These matters are complex and cannot be adequately covered in this manuscript. However, the principal citations listed in the introduction provide insights and unresolved challenges in designing and operating an economical biosecure shrimp production system (Fig. 2). More clearly stated, the institution of biosecurity protocols is having an indirect but substantial impact on traits selected for genetic selection as well as feeds and feeding and water quality. Biosecurity is and will remain an absolutely essential part of intensive animal production systems. Aquaculture remains well behind the poultry industry in its understanding of diseases/pathogens and efficient methods of biosecurity. Acknowledgements We acknowledge funding from the USDA/CSREES Contract Number 99-38808-7431, which supports the U.S. Marine Shrimp Farming Program.
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References Swimming through Troubled Water, 1995. In: Browdy, C.L., Hopkins, J.S. (Eds.), Proceedings of the Special Session on Shrimp Farming. Aquaculture, 1–4 February 1995, San Diego, California. World Aquaculture Society, Baton Rouge, Louisiana, United States, p. 253. Browdy, C.L., Bratvold, D., 1998. Preliminary Development of a Biosecure Shrimp Production System. In: Moss, S.M. (Ed.), Proceedings of the US Marine Shrimp Farming Program Biosecurity Workshop, 14 February 1998, Hawaii, United States. The Oceanic Institute, Hawaii, United States, pp. 19–38. Controlled and Biosecure Production Systems: Evolution and Integration of Shrimp and Chicken Models. In: Bullis, R.A., Pruder, G.D. (Eds.), Proceedings of a Special Session, World Aquaculture Society, 27–30 April 1999, Sydney, Australia. The Oceanic Institute, Hawaii, United States, 2000, p. 106. Gjedrem, T., Salte, R., Gjoen, H.M., 1991. Genetic variation in susceptibility of Atlantic salmon to furunculosis. Aquaculture 97, 1–6. Glick, B., Chang, T.S., Japp, R.G., 1956. The bursa of Fabricius and antibody production. Poult. Sci. 35, 224–225. Guillermo, Z., 2000. Biosecurity in the Poultry Industry. In: Bullis, R.A., Pruder, G.D. (Eds.). Proceedings of a Special Session, Controlled and Biosecure Production Systems: Evolution and Integration of Shrimp and Chicken Models, World Aquaculture Society, 27–30 April 1999, Sydney, Australia. The Oceanic Institute, Hawaii, United States pp. 75–78. Lee, C.-S., O’Bryen, P.J. (Eds.), Biosecurity in Aquaculture Production Systems: Exclusion of Pathogens and Other Undesirables, The World Aquaculture Society, Baton Rouge, Louisiana 70803, United States, 2003, p. 188. Moss, S.M., Reynolds, W.J., Mahler, L.E., 1998. Design and Economic Analysis of a Protogype Biosecure Shrimp Growout Facility. In: Moss, S.M. (Ed.), Proceedings of the US Marine Shrimp Farming Program Biosecurity Workshop, 14 February 1998, Hawaii, United States. The Oceanic Institute, Hawaii, United States, pp. 5–14. Moss, S.M., 2002. Marine Shrimp Farming in the Western Hemisphere: Past Problems, Present Solutions, and Future Visions. In: Lee, C.-S., P.J. O’Bryen (Eds.), Proceedings of a workshop held by the Oceanic Institute, 12–15 February 2001, Honolulu, Hawaii, United States. Aquaculture Growout Systems-Challenges and Technological Solutions, Reviews in Fisheries Science, 101 (3–4), 601–620. Pardue, S.L., 2000. A Half-Century of Innovation in Poultry Production. In: Bullis, R.A., Pruder, G.D. (Eds.), Proceedings of a Special Session, World Aquaculture Society, 27–30 April 1999, Sydney, Australia. Controlled and Biosecure Production Systems: Evolution and Integration of Shrimp and Chicken Models. The Oceanic Institute, Hawaii, United States pp. 85–95. Pruder, G.D., Brown, C.L., Sweeney, J.N., Carr, W.C., 1995. High Health Shrimp Systems: Seed Supply-Theory and Practice. In: Browdy, C.L., Hopkins, J.S. (Eds.), Proceedings of the Special Session on Shrimp Farming Aquaculture 1995. Proceedings of the Special Session on Shrimp Farming, 1–4 February 1995, San Diego, California. Swimming Through Troubled Water. World Aquaculture Society, Baton Rouge, Louisiana, United States pp. 40–52. Tave, D., 1993. Genetics for Fish Hatchery Managers, Van Nostrand Reinhold, New York, p. 415. Wyban, J.A., Swingle, J.S., Sweeney, J.N., Pruder, D.G., 1993. Specific pathogen free Penaeus vannamei. J. World Aquacult. Soc. 24 (1), 39–45.
Biosecurity: application in aquaculture Gary D. Pruder∗ The Oceanic Institute, 41-202 Kalanianaole Highway, Suite 9, Waimanalo, HI 96795 USA
Abstract The introduction and discussion of biosecurity in aquaculture occurred in 1997 in a World Aquaculture Society (WAS) Special Session titled, ‘Sustainable Shrimp Farming: Emerging Technologies and Products for Biosecurity and Zero Discharge.’ By 2003, proceedings of several workshops were published which offer very valuable information on the need, application and problems with biosecurity. These published proceedings are identified and discussed. While biosecurity is relatively new to aquaculture, other agricultural animal production systems, namely poultry, have fully developed and finely tuned biosecurity procedures in place. The adoption of biosecurity protocols in shrimp aquaculture has required significant changes in the shrimp stocks and adjustments in feeds and feeding, genetic traits for selection, and overall production procedures. Biosecurity in aquaculture is a maturing activity, still in need of improved information on diagnostics, disease transmission, clean up and eradication. Biosecurity, health, nutrition genetics and environmental quality must be integrated to achieve a uniform and low cost product on demand. © 2004 Elsevier B.V. All rights reserved. Keywords: Poultry; Shrimp; SPF; Water Exchange; Feed Nutrition; Microbes
1. Introduction The invitation from Dr. Tony Schurr to present a paper on Biosecurity in Aquaculture was directed to the Oceanic Institute (OI). Having been involved in the intricacies of recognizing the need for and initiating initial applications of biosecurity in marine shrimp culture and knowing that the audience would be largely engineers, I personally accepted the invitation. The preparation of this manuscript led me to three principal references which together summarize biosecurity applications in aquaculture and events leading up to the ∗
Corresponding author. Tel.: +1 808 259 3102; fax: +1 808 259 5971. E-mail address: [email protected] (G.D. Pruder).
0144-8609/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaeng.2004.05.002
4
G.D. Pruder / Aquacultural Engineering 32 (2004) 3–10
need for biosecurity in marine shrimp farming. The references are listed below with a brief description of their content and contributors. The special session was conceived and planned at a time when the shrimp industry worldwide was suffering severe mortality problems related to diseases (Browdy, C.L. and Hopkins, J.S., 1995 (Editors)). Twenty-two scientists worldwide, selected for their expertise across the whole range of sustainability problems, were invited to prepare and present manuscripts. Each of the authors made significant contribution of time and expertise. The results of their dedication provide a valuable compendium of some of the best and latest information on shrimp farming for researchers, and producers addressing recent sustainability problems. For a number of years, investigators dedicated to the development of advanced shrimp farming technologies have drawn comparison, with agricultural animal husbandry industries (Bullis, R.A. and Pruder, G.D., 2000 (Editors)). Principal comparisons have centered on the integration of genetically-improved, high-health stocks, advanced feeds and feeding methods and disease control and biosecurity. The planners and organizers of the special session offered direct comparisons by alternating presentations by chickens and shrimp experts, followed by a round table discussion. Of the ten papers, four were by industry and university chicken experts, the remaining six were by research scientists of the U.S. Marine Shrimp Farming Consortium. This workshop was organized by the Aquaculture Exchange Program of OI and funded by the Department of Commerce (Lee, C.-S. and O’Bryen, P.J., 2003 (Editors)). Scientists worldwide were identified and invited to participate based upon their expertise in biosecurity measures used against the spread of bacterial disease, viral diseases and parasites in production systems for major aquaculture species. The workshop was organized to allow information exchange regarding regulations and management practices in preventing disease outbreaks in finfish, crustaceans and mollusks. Sixteen papers and a summary discussion are included in the publications. Discussions focused on biosecurity basics, type of diseases that should be addressed through biosecurity, detecting and eliminating disease transmission, non-fish disease vectors and the effectiveness of regulatory enforcement. The quality of this information should be instructive for those wishing a sound understanding of principles, practices and weaknesses of current efforts in aquaculture. Therefore, this manuscript will highlight various aspects and attempt to show that, while biosecurity is a vital activity, it is one of several vital activities that are interactive and interdependent. These other activities are genetics, nutrition, health and improved production systems. The poultry industry is used as a cornerstone or point of departure for application of biosecurity in aquaculture. Perhaps more than any other segment of animal agriculture poultry has relied on technological innovations made possible through scientific discovery. Poultry remains a viable model for aquacultural development. It is noted that the poultry model extends beyond science and technology. Although not a core subject, this manuscript highlights various marketing, product forms (over 3,000) and product differentiation are crucial aspects whose effect may have exceeded technology in underpinning the world competitiveness of the poultry industry. A successful aquaculture industry in the United States cannot be built solely on technology.
G.D. Pruder / Aquacultural Engineering 32 (2004) 3–10
5
2. Biosecurity Guillermo Zavala (2000) defined biosecurity in the poultry as an essential group of tools for the prevention, control and eradication of economically important infectious diseases in poultry. Biosecurity in aquaculture has been defined as the sum of all procedures in place to protect living organisms from contracting, carrying, and spreading diseases and other non-desirable health conditions (Moss et al., 1998). As applied to aquaculture, the scope of biosecurity has yet to be adequately defined but its activities will be comprised of preventive medicine, adequate diagnosis, contain outbreaks that occur, disinfection and eradication. Biosecurity is a shared responsibility, in that each individual in the process of animal production plays a different but critical role in the implementation of an overall program. Any failure in the chain of process will undercut the overall effort to establish and maintain biosecurity. In general, biosecure operations should have a defined structure and barriers, such as fences and gates in place. The faculty should be constructed with materials that can be disinfected easily should a disease outbreak occur and is free from unauthorized access such as vehicles or people. Structurally, it should also prevent the escape of target animals and the entry of other animals. It should be sited away from hazards that are potential sources of infection or contamination. Untreated surface water should not be used as the source water because it may contain pathogens. The ideal system should have appropriate back-up water, life support systems and operational procedures that allow one-way flow, so that nothing can be returned to the facility without disease screening. Biosecurity is practiced at three intensity levels: (1) specific pathogen-free (free of defined infectious agents) for vaccine and laboratory reagent production (2) primary breeding industry, (3) commercial grower level. In general terms the resources for disease control involve one or more of the following aspects—quarantine; control traffic of personnel, vehicles and equipment; vaccination and/or medication; diagnostic testing; depopulations and eradication.
3. The poultry case In 1948, it took 94 days to grow a four pound chicken and the feed conversion ratio was 3.85/1. Today the same weight chicken takes 38 days with a feed conversion of 1.80. In other words, today’s chicken grows more than twice as fast on less than half the feed. These resulted through an integration of health, biosecurity, improved production systems, nutrition and genetics. Without biosecurity this revolution could not have occurred. The half century of innovation in poultry productions is an excellent example and perhaps a model for aquaculture. Samuel L. Pardue (2000) provided an instructive review, from which the following extracts are highlighted. ‘Within the past half century, a barnyard enterprise has evolved into a dynamic global poultry industry. Through the adoption of management philosophy that embraces technology, the poultry industry has witnessed advances in efficiency and uniformity of production that are unparalleled.’
6
G.D. Pruder / Aquacultural Engineering 32 (2004) 3–10
The United States alone produced nearly a quarter of the 51 M mt of chicken produced around the world. There were major forces that contributed to the development of the poultry industry including expansion, consolidation, integration, scale, marketing, product differentiation, overall automation, and scientific discovery. Repeating a point made in the introduction. However, for the purposes of this paper on biosecurity, this manuscript concentrates only on scientific discovery. Two major disciplines, genetics and nutrition, have had a mutually beneficial relationship with poultry for much of this century. ‘Several characteristics have contributed including relatively short generation time, small body mass, low cost of maintenance and a non-ruminant digestive system. Understanding of the nutritional requirements of the chick probably exceeds that of all other animals including humans. Bruce Glick’s discovery of bursal-derived lymphocytes (B cells) in the chicken revolutionized our understanding of humoral immunity Glick et al. (1956). The poultry industry is most advanced in the understanding and exploitation of immunosuppressive diseases.’ Vaccines, thus, play a cornerstone role in modern poultry production. However, the largest single contributor to advances in poultry production is selective breeding supported by nutrition, management and health activities. Milton L. Boyle III, stated that, “the similarities between the genetics of poultry and shrimp are striking and include economic traits of interest as well as their heritabilities and genetic interactions. Poultry breeding involves intense and sophisticated selection schemes, even to the point of niche marketing and multiproduct development. Biosecurity is vital and exists at a stringent level at the breeding facilities, where disease outbreaks would be catastrophic.” Importantly, very early chicken breeding efforts initially targeted growth rates and disease resistance. ‘Broiler commercial traits now include growth rate, feed efficiency, meat yield, body conformation, livability, skeletal integrity and feathering. Reproductive traits include hatching egg production, age at first egg, egg size, egg shape, breeder livability, fertility, and hatchability. In many cases the traits are antagonistic to each other so that balanced breeding schemes are utilized.’ Specific efforts to breed for disease resistance resulted in much slower growing chickens. The advent of vaccines and the development and exploitation biosecurity protocols replaced the much costlier and unreliable genetic selection for disease resistance. ‘Decades of research in poultry diseases have rendered invaluable information that is now used by the poultry industry on a daily basis. Many microorganisms have been well characterized in their pathogenesis, even to the molecular level. This was essential for the development of vaccines and diagnostic tools. Without the research and understanding of such poultry pathogens it would have been impossible to control them. The parallel between the poultry industry a generation ago and aquaculture are more than apparent. Whether aquaculture can utilize the poultry model remains to be seen. The poultry model does, however, raise intriguing questions as to the future of this growing aquaculture agri-business.’ 4. The marine shrimp case 4.1. Specific pathogen-free (SPF) shrimp In the 1990s shrimp farms around the world were experiencing severe economic losses due to low yields and high mortalities. The problems cut across national boundaries, species,
G.D. Pruder / Aquacultural Engineering 32 (2004) 3–10
7
culture system and environmental conditions. The principal disease vector appeared to be diseased or disease carrying shrimp seed, both wild and hatchery-reared. Farms in the United States that were using high-health shrimp provided by OI as part of the U.S. Marine Shrimp Farming Consortium (USMSFC), were seemingly unaffected. However, the import of foreign produced shrimp seed to both South Carolina and Texas resulted in severe crop loss. The point had been made that bringing diseased or disease carrying shrimp onto farms was an invitation to disaster. In 1993, Wyban et al. differentiated between high-health and specific pathogen-free broodstock and seed, commonly used terms that are poorly understood and often misused. It was explained that reference to high-health stock, rather than SPF, reflects a loss of control over the health status of the stock. In this paper, SPF stocks relate only to stocks retained in the breeding center that have already undergone rigorous quarantine and screening efforts. Once stocks leave the breeding center, they are considered high-health, which means they are free of certain pathogens to the best of our ability and understanding. The process of establishing SPF stocks is shown (Fig. 1) and the list of specific pathogens is also shown (Table 1). The cornerstone of the emerging genetic improvement program is SPF stock gathered from around the world. Genetic research on shrimp indicates that their heritability estimates for commercially important traits are similar to poultry. This indicates the potential for genetic advance in shrimp is formidable. Rapid progress is being made in breeding shrimp for very high growth rates at very high densities.
Fig. 1. Development of SPF shrimp.
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G.D. Pruder / Aquacultural Engineering 32 (2004) 3–10
Table 1 Working list of specific pathogens for SPF shrimp Pathogen type
Pathogen/pathogen group
Pathogen category
TSV–picornavirus WSSV–nimavirus (new family) YHV/GAV/LOV3 –roniviruses (new family) IHHNV–systemic parvovirus BP–occluded enteric baculovirus MBV–occluded enteric baculovirus BMN–nonoccluded enteric baculovirus HPV–enteric parvoviruses
C-1 C-1 C-1 C-2 C-2 C-2 C-2 C-2
NHP–alpha proteobacteria
C-2
Microsporidians Haplosporidians Gregarines
C-2 C-2 C-3
Viruses
Procaryote Protozoa
Pathogen category with C-1 pathogens defined as excludable pathogens that can potentially cause catastrophic losses in one or more American penaeid species; C-2 pathogens cause economically significant disease and are excludable; and C-3 pathogens cause less serious disease, but should be excluded from breeding centers, hatcheries, and some types of farms.
Although vaccines, medicated feeds, and immunostimulants are effective in combating some pathogens in other meat-producing industries, they are either unavailable to shrimp farmers or their efficacy is unproven. Various strategies are being employed to mitigate the risk of disease including, high-health seed, reduced water exchange rates and screening influent water. Genetic selection can enhance disease resistance in farmed plants and animals, including fish (Gjedrem et al., 1991). However, the heritability estimate for disease resistance in white shrimp was 0.09 ± 0.03. Tave (1993) reported that heritability estimates less than 0.15 are difficult to improve by selection. Nonetheless, OI was able to increase resistance to Taura syndrome virus (TSV) in a few generations. However, note that subsequently TSV now occurs as TSV 1, TSV 2, and TSV 3, due to natural phenomenon for which the selected shrimp have less resistance. In light of the limitations in breeding for disease resistance, selective breeding should not be perceived as a panacea to the health problems plaguing the shrimp industry. In the absence of vaccines and effective selection for disease resistance, the shrimp industry has two principal opportunities to control disease—high-health stocks and biosecurity. 4.2. Zero-water exchange The second most likely source of disease and/or disease causing organism is water exchange. The using of raw or untreated make up water is responsible for continued disease problems when ponds are stocked with high-health shrimp seed. Fill and exchange water needs to be disinfected. The cost of water disinfection quickly drove production system research under the zero-water exchange banner. Biosecure shrimp production systems stocked
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Fig. 2. Growout and system management.
with high-health seed represent an emerging technology with an environmentally sustainable and economically viable alternative to conventional shrimp culture. Such systems have been described previously (Moss, 2002; Browdy and Bratvold, 1998; Pruder et al., 1995; Wyban et al., 1993). 4.3. Feed, nutrition and microbes The restricted use of water exchange rippled through shrimp growout technologies causing major changes in feeds and feeding and the maintenance of mixed microbial populations. These matters are complex and cannot be adequately covered in this manuscript. However, the principal citations listed in the introduction provide insights and unresolved challenges in designing and operating an economical biosecure shrimp production system (Fig. 2). More clearly stated, the institution of biosecurity protocols is having an indirect but substantial impact on traits selected for genetic selection as well as feeds and feeding and water quality. Biosecurity is and will remain an absolutely essential part of intensive animal production systems. Aquaculture remains well behind the poultry industry in its understanding of diseases/pathogens and efficient methods of biosecurity. Acknowledgements We acknowledge funding from the USDA/CSREES Contract Number 99-38808-7431, which supports the U.S. Marine Shrimp Farming Program.
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References Swimming through Troubled Water, 1995. In: Browdy, C.L., Hopkins, J.S. (Eds.), Proceedings of the Special Session on Shrimp Farming. Aquaculture, 1–4 February 1995, San Diego, California. World Aquaculture Society, Baton Rouge, Louisiana, United States, p. 253. Browdy, C.L., Bratvold, D., 1998. Preliminary Development of a Biosecure Shrimp Production System. In: Moss, S.M. (Ed.), Proceedings of the US Marine Shrimp Farming Program Biosecurity Workshop, 14 February 1998, Hawaii, United States. The Oceanic Institute, Hawaii, United States, pp. 19–38. Controlled and Biosecure Production Systems: Evolution and Integration of Shrimp and Chicken Models. In: Bullis, R.A., Pruder, G.D. (Eds.), Proceedings of a Special Session, World Aquaculture Society, 27–30 April 1999, Sydney, Australia. The Oceanic Institute, Hawaii, United States, 2000, p. 106. Gjedrem, T., Salte, R., Gjoen, H.M., 1991. Genetic variation in susceptibility of Atlantic salmon to furunculosis. Aquaculture 97, 1–6. Glick, B., Chang, T.S., Japp, R.G., 1956. The bursa of Fabricius and antibody production. Poult. Sci. 35, 224–225. Guillermo, Z., 2000. Biosecurity in the Poultry Industry. In: Bullis, R.A., Pruder, G.D. (Eds.). Proceedings of a Special Session, Controlled and Biosecure Production Systems: Evolution and Integration of Shrimp and Chicken Models, World Aquaculture Society, 27–30 April 1999, Sydney, Australia. The Oceanic Institute, Hawaii, United States pp. 75–78. Lee, C.-S., O’Bryen, P.J. (Eds.), Biosecurity in Aquaculture Production Systems: Exclusion of Pathogens and Other Undesirables, The World Aquaculture Society, Baton Rouge, Louisiana 70803, United States, 2003, p. 188. Moss, S.M., Reynolds, W.J., Mahler, L.E., 1998. Design and Economic Analysis of a Protogype Biosecure Shrimp Growout Facility. In: Moss, S.M. (Ed.), Proceedings of the US Marine Shrimp Farming Program Biosecurity Workshop, 14 February 1998, Hawaii, United States. The Oceanic Institute, Hawaii, United States, pp. 5–14. Moss, S.M., 2002. Marine Shrimp Farming in the Western Hemisphere: Past Problems, Present Solutions, and Future Visions. In: Lee, C.-S., P.J. O’Bryen (Eds.), Proceedings of a workshop held by the Oceanic Institute, 12–15 February 2001, Honolulu, Hawaii, United States. Aquaculture Growout Systems-Challenges and Technological Solutions, Reviews in Fisheries Science, 101 (3–4), 601–620. Pardue, S.L., 2000. A Half-Century of Innovation in Poultry Production. In: Bullis, R.A., Pruder, G.D. (Eds.), Proceedings of a Special Session, World Aquaculture Society, 27–30 April 1999, Sydney, Australia. Controlled and Biosecure Production Systems: Evolution and Integration of Shrimp and Chicken Models. The Oceanic Institute, Hawaii, United States pp. 85–95. Pruder, G.D., Brown, C.L., Sweeney, J.N., Carr, W.C., 1995. High Health Shrimp Systems: Seed Supply-Theory and Practice. In: Browdy, C.L., Hopkins, J.S. (Eds.), Proceedings of the Special Session on Shrimp Farming Aquaculture 1995. Proceedings of the Special Session on Shrimp Farming, 1–4 February 1995, San Diego, California. Swimming Through Troubled Water. World Aquaculture Society, Baton Rouge, Louisiana, United States pp. 40–52. Tave, D., 1993. Genetics for Fish Hatchery Managers, Van Nostrand Reinhold, New York, p. 415. Wyban, J.A., Swingle, J.S., Sweeney, J.N., Pruder, D.G., 1993. Specific pathogen free Penaeus vannamei. J. World Aquacult. Soc. 24 (1), 39–45.