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Aquaculture: Environmental, toxicological, and health issues
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Int. J. Hyg. Environ. Health 212 (2009) 369–377 www.elsevier.de/ijheh
Aquaculture: Environmental, toxicological, and health issues David W. Cole, Richard Cole, Steven J. Gaydos, Jon Gray, Greg Hyland, Mark L. Jacques, Nicole Powell-Dunford, Charu Sawhney, William W. Au Department of Preventive Medicine and Community Health, 700 Harborside Drive, University of Texas Medical Branch, Galveston, TX 77555-1110, USA Received 26 February 2008; received in revised form 10 July 2008; accepted 15 August 2008
Abstract Aquaculture is one of the fastest growing food-producing sectors, supplying approximately 40% of the world’s fish food. Besides such benefit to the society, the industry does have its problems. There are occupational hazards and safety concerns in the aquaculture industry. Some practices have caused environmental degradation. Public perception to farmed fish is that they are ‘‘cleaner’’ than comparable wild fish. However, some farmed fish have much higher body burden of natural and man-made toxic substances, e.g. antibiotics, pesticides, and persistent organic pollutants, than wild fish. These contaminants in fish can pose health concerns to unsuspecting consumers, in particular pregnant or nursing women. Regulations and international oversight for the aquaculture industry are extremely complex, with several agencies regulating aquaculture practices, including site selection, pollution control, water quality, feed supply, and food safety. Since the toxicological, environmental, and health concerns of aquaculture have not been adequately reviewed recently, we are providing an updated review of the topic. Specifically, concerns and recommendations for improving the aquaculture industry, and for protection of the environment and the consumers will be concisely presented. r 2008 Elsevier GmbH. All rights reserved. Keywords: Aquaculture; Fish; Nutrition; Occupational health; Pesticides; Public health
Introduction Husbandry of aquatic organisms has been practiced through the ages (Bardach et al., 1972). Oyster culture, for instance, thrived in ancient Rome and Gaul (Bardach et al., 1972). Humankind has always been in search of more efficient food-production methods for ever increasing human consumption. In addition, many fish are produced in hatcheries for sport fishing and repletion of wild stock, such as trout, largemouth bass, Corresponding author. Tel.: +1 409 772 1545; fax: +1 409 772 9108. E-mail address: [email protected] (W.W. Au).
1438-4639/$ - see front matter r 2008 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijheh.2008.08.003
and salmon. Thus, one would recognize that aquaculture not only feeds the human population, but also provides a vital service to replenish certain species. Since the 1960s, aquaculture production have increased dramatically due to much improved conditions such as water quality, disease control, nutritionally complete feeds, and the development of improved stocks through selective breeding, hybridization, and the application of molecular genetics technology (Stickney, 1994). Globally, farmed fish production more than doubled from 1987 to 1997 at a rate of 9% per year (Englehaupt, 2007) and aquaculture is becoming a major industry that provides approximately 43% of seafood to the consumers (FAO, 2006, 2007a). China
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remains the largest producer with reported fisheries production of 47.5 million tons in 2004 providing an estimated domestic food supply of 28.4 kg per capita as well as production for export and non-food purposes, followed by India and the Philippines (FAO, 2006). The United States (US) ranks third in the world in consumption of seafood and eleventh in the world in aquaculture production, therefore the US has historically had to rely on high levels of seafood imports (Goldberg et al., 2001). It may appear that aquaculture is highly beneficial and has no drawbacks but that is far from accurate. The aquaculture industry, like other industries, has its share of occupational hazards, safety concerns, and risks to the individual health of the worker. There also exist several deleterious effects on the environment from aquaculture. Farmed fish, although presumably safer from contamination than wild fish, have, in fact, higher body burden of certain toxic chemicals that may present health concerns to unsuspecting consumers. On the other hand, a major benefit of farmed fish is that they provide a good and low-cost source of polyunsaturated fatty acids (PUFA’s) which can enhance cardiovascular health in humans. Regulations and international oversight for the aquaculture industry are extremely complex, with several agencies attempting to regulate aquaculture practices, including site selection, pollution control, water quality, feed supply, and food safety. These practices differ from country to country and sometimes between states and territories within a country. However, there are ongoing efforts to standardize practices across borders and harmonize international regulations. The concerns and recommendations for improving the aquaculture industry are of constant interest. From our literature search in PubMed, we recognized that there are only a handful of review papers on the general topic during the last two years. The majority of them, however, focused on infection and microbiological problems. Therefore, an updated review of environmental, toxicological and health concerns of aquaculture is needed. Our current review has also included recent publications on the topic.
Genetic manipulation in aquaculture and the ecological impact on the environment The use of technologies and breeding programs has generated aquaculture species that are both more practical and economical to produce. For example, male tilapia grows faster than females, making it the preferred sex for commercial production. A YY male genotype sires progeny that are nearly all males (Muir, 2005). In contrast, rainbow trout are selected for an all
female crop for better growth rate and less risk of precocious maturity (Muir, 2005). Gynogenesis inbreeds these female fish by using irradiated sperm so the progeny have no paternal genes making an all female generation (Halvorson and Quezada, 1999). Atlantic salmon raised in British Colombia are sterile triploid females to prevent their breeding with wild Pacific salmon in the event of an escape (Hulata, 2001; Reichhardt, 2000). Salmons are sterilized by heating or providing a pressure shock to the eggs shortly after fertilization to retain an extra set of chromosomes (Reichhardt, 2000). Further sex-control technologies include endocrine treatments for sex reversal (Hulata, 2001). Potential environmental and genetic hazards exist if modified fish are released into the wild, e.g. unintentionally as a result of escape (Stokstad, 2002; MauryBrachet et al., 2008). These fish that are then introduced into the wild may spread unique diseases and parasites (Beveridge, 1990). An example is a recent report indicating that sea lice from farmed salmon can possibly cause certain native salmons in British Columbia to plummet by 99% within eight years (Krkosek et al., 2007). The ecological impacts are also centered on heightened predation and altered population or ecosystem secondary to the escaped fish’s activities (Goldberg et al., 2001). The modified fish may become established where that species was not previously present. For instance, a fish genetically altered with antifreeze protein could migrate ‘‘upstream’’ to a colder environment where the wild species cannot survive and displace the endogenous species. The genetically altered fish could reproduce with the feral type resulting either in a more robust fish that disrupts the environment or in poorly fit fish causing a gradual extinction of the species (Goldberg et al., 2001). The development of beneficial transgenic organisms requires the insertion of appropriate genes during the blastocyst stage of embryonic development. Genes that can provide highly desirable benefits include: growth hormone, freeze protection and disease resistant genes (Halvorson and Quezada, 1999). Transgenic fish have been produced in Atlantic salmon, Coho salmon, Chinook salmon, rainbow trout, cutthroat trout, tilapia, striped bass, channel catfish, common carp, and Indian major carps (FAO, 2007b). For example, Aqua Bounty Farms Inc., of Waltham Massachusetts has developed a transgenic Atlantic salmon that can grow up to six times as fast as ordinary farm-raised salmon after the introducing of a growth hormone and promoter sequences from a Chinook salmon (Stokstad, 2002). Although commercial production of transgenic fish has been seriously considered (Hu et al., 2007), transgenic fish has not been approved by the US Food and Drug Administration for human consumption yet (Muir and
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Howard, 1999; FAO, 2007b; Hallerman, Personal communication).
Occupational hazards of aquaculture The occupational hazards, safety concerns, and risks to health in the aquaculture industry can vary considerably based on the types of operation, scale of production, and even the specific species of interest (EFSA, 2005). In 2006, the non-fatal occupational injury incidence rate for aquaculture (injuries per 100 full-time workers) was 6.8 (Survey of Occupational Injuries and Illnesses, Bureau of Labor Statistics, USA). In comparison, terrestrial crop production was 5.3 and animal production was 7.8. Aquaculture occupational hazards and risks to health can generally be categorized into those concerning physical work hazards, chemical and toxic exposures, and risks associated with infectious disease. Regarding the physical work environment, risks concerning machinery and tool use are similar to that of terrestrial agriculture. High-torque capacity tractors used in aquaculture, for example, are subject to the same roll-over protection (Occupational Safety and Health Administration (OSHA) compliance standards) as farm tractors (OSHA, 2007). Electrocution and high-voltage electrical accidents are also of concern, particularly due to the proximity of water (Durborow, 1999). Other hazards might include drowning, musculoskeletal injuries from repetitive lifting of heavy cages and nets, over-use injuries like tenosynovitis from repetitive motion tasks, and long-term exposure in extreme environments of sunlight, wind, cold, and water (Douglas, 1995). Therefore, personal flotation devices (PFDs), thermal protection for cold environment and foam-padded PFDs against chest and rib injuries are needed (Douglas, 1995). Divers are also at risk for decompression sickness. Such cases have been reported with multiple descents and ascents (deemed ‘‘yo-yo’’ diving) to clear dead fish from cages, even in relatively shallow water of less than 20 m (Douglas, 1991). Toxic exposures are of concern to aquaculture workers because they can be exposed to unique and toxic chemicals, e.g. Nessler’s Reagent which is used to test for the presence of ammonia contains potassium hydroxide, mercuric iodide, and potassium iodide (Durborow, 1999). Hydrogen sulfide (H2S) occurs naturally from organic breakdown, often during anaerobic reactions on pond bottoms (Durborow, 1999). H2S can cause anoxic brain injury and unconsciousness at high levels and is predominantly a mucous membrane and respiratory irritant at lower levels (Kuschner and Blanc, 2007). In one unfortunate case, the autopsies of three drowned aquaculture workers reveled sublethal
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H2S levels, and this exposure was thought to have contributed to their drownings (Durborow, 1999). Toxicity information on products is typically focused on single chemicals. In aquaculture, combining the use of multiple toxic products can be a common practice. Such practices can produce toxic by-products and harmful gases from chemical reactions, and the health risk to workers under this condition is not known. There are health risks to workers associated with microbial exposure and processes related to the prevention of infectious diseases in aquaculture species. For example, with respect to prevention, accidental autoinoculation or self-injection with antimicrobials, immunizations, or veterinary biologics carries the potential to produce a range of pathology in the worker from local tissue reaction to full anaphylaxis (Douglas, 1995; Durborow, 1999). Aquaculture workers can be exposed to uncommon microbes including bacteria, viruses, algae, and parasites potentially causing zoonotic disease or emerging infections. For example, four separate tilapia fish processors developed health complications subsequent to infection with Streptococcus iniae, a fish pathogen not previously reported to be a cause of disease in humans (CDC, 1996; Garrett et al., 1997). As published by Durborow (1999), many other fish pathogens are known to be contagious to humans, including several species of the genera Mycobacterium and Vibrio (especially M. marinum, V. vulnificus, and V. parahemolyticus), as well as species of Streptococcus, Aeromonas, Erysipelothrix, and Pseudomonas. A more inclusive list would also include parasites (nematodes, trematodes, and flukes), protozoans, and dinoflagellates.
Environmental impact from aquaculture Environmental degradation from aquaculture practices has been reported. The negative effects include organic pollution and eutrophication, a buildup of excess nutrients (primarily organic nitrogen and phosphorus) and wastes in an ecosystem. These problems together with chemical pollution can cause algal bloom, depletion of oxygen, reduction in water quality, death of corals and habitat destruction (Boesch et al., 2001; Aubin, 2006). Certain microorganisms that thrive in this adverse environment are directly harmful to fish through biologic and neurologic toxins (Aubin, 2006). These detrimental effects are usually localized to surrounding regions and can be transitory. Therefore, good management protocols can be used to minimize the effects, e.g. situate net pens in areas with high natural flushing rates, periodic fallowing between cycles of production, use of seaweed biofilters and use of mollusk-farming to remove organic nitrogen from the water (Kaspar et al., 1985; Chopin et al., 1999; Debruyn et al., 2006).
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A large quantity of wild-caught fish has been used as feeds for aquaculture. However, when these forage fish stocks are heavily harvested, it can directly affect marine ecosystems negatively by the reduction of food available for predators (Naylor et al., 2000). Therefore, alternative sources of feed are being considered. Chemicals used in aquaculture can also cause pollution in the environment. These chemicals can come from antibiotics, pesticides, herbicides, hormones, anesthetics, pigments, minerals, and vitamins (Goldberg et al., 2001; JSA, 2007). There is limited data on the extent of antibiotic use by producers outside of the USA but they may rely on antibiotics to a greater extent (Mellon et al., 2001). A concern about antibiotic use is that it may affect un-intended species leading to antibiotic resistance and other toxic effects (Brown, 1989). This may have been a reason why some pathogens have become resistant to many drugs that are used in aquaculture (Dixon, 2000). Herbicides are used to control aquatic weeds, algal blooms, and fouling organisms. Net pen operators often treat their nets with paints that contain copper-based algaecide. These and other compounds appear relatively safe when applied in approved conditions; however, there are concerns that a spill of these chemicals can cause irreversible damage to the environment (Eisler, 1998). Diseases and parasites for aquaculture can be deleterious in wild fish stock. Parasites may serve as a host for other lethal diseases such as infectious salmon anemia (ISA) which has been detected in both escaped farmed and wild fish (FWS/NOAA, 2000). Another example of parasite introductions into the environment is sea lice which is a serious problem affecting salmon farms and can also impact wild salmon migrating through coastal waters (Finstad et al., 2000; Krkosek et al., 2007). A concern that attracts a lot of attention is the alteration and destruction of natural habitats. Habitat modification is an important aspect for increasing aquaculture productivity. It includes direct habitat conversion and predator-control programs (Goldberg et al., 2001). In some areas, flow and composition of rivers is altered because of the biological processes of non-native species. Farmed species may feed on and cause local extinction of certain plant and aquatic species. Clustering or poor sitting of aquaculture operations can also obstruct wild animals’ use of their natural surroundings including the passage of migrating fish (Goldberg et al., 2001). Other organisms may be introduced or removed from areas of aquaculture therefore transforming the environment food web and overall cycle (Phillips, 1990). Aquaculture has some environmentally positive effects as well. Aquaculture can reduce the dependence on natural stocks as well as genetic conservation of endangered species. Aquaculture is also useful in areas
of limited aquatic life, by enrichment of the local water column. Aquaculture indirectly benefits the environmental by providing a method to convert agriculture waste into high-quality fish protein, by enriching pond mud for use as fertilizer and for improving soil quality on crop land (Muir, 1999).
Nutritional value and comparison with wild seafood Fish muscle is an abundant source of PUFA’s in the human diet, especially n-3 and n-6, or more commonly known as omega-3 and omega-6, fatty acids. It is believed that two of the very long-chain omega-3 fatty acids, eicosapentaenoic acid, and docosahexaenoic acid, specifically may lower the risk of coronary heart disease in humans (van Vliet and Katan, 1990). Fish is the major dietary source of these two important fatty acids in humans. Therefore, the American Heart Association (AHA) recommends that healthy adults eat at least two servings of fish per week. The AHA also recommends that individuals with coronary heart disease need 1 g of combined eicosapentaenoic acid and docosahexaenoic acid per day; while those who have elevated triglycerides may need 2–4 g per day (AHA, 2007). Such benefit from fish consumption makes comparing the composition of these fatty acids in fish muscle between wild and farmed fish an important investigation. Among trout, salmon and sea bass, higher levels of beneficial omega-3 to omega-6 fatty acid ratios were found in farmed compared to wild fish (Suzuki et al., 1986; van Vliet and Katan, 1990; Alasalvar et al., 2002). In addition, the beneficial fatty acid composition of farmed fish can be increased through the manipulation of their diet (Bell et al., 2001). For example, Alasalvar et al. (2002) showed that feeding fish with feed that contained higher levels monoenoic acids led to higher levels of these fatty acids in fish tissues. Similar observations were made with oleic acids (Alasalvar et al., 2002). More recently, fish feeds have also included the use of vegetable sources such as soybeans, rapeseed, and wheat (Cahu et al., 2004). The benefits and limitations on nutritional values from the use of the modified fish feed needs to be evaluated. Another topic which has been scientifically studied is the area of trace mineral and vitamin contents in fish. Nettleton and Exler (1992) reported that, among finfish, the only difference across all species was greater niacin content in raw samples of farmed versus wild trout. This difference, however, was not seen among the corresponding cooked samples of trout. Alasalvar et al. (2002) examined several essential and non-essential minerals in fish samples and found higher levels of Fe,
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Al, Ti, and V in wild sea bass compared to their farmed counterparts.
Contamination in fish and health issues Consumers may select farmed fish for meal as a healthier and safer alternative to wild fish because aquaculture is presumably located away from industries that generate contaminated air and water. However, consumers have been surprised to find that several natural and man-made toxic substances are at higher concentrations in farmed than wild fish (Table 1). Some examples of man-made contaminants in farmed fish are: pesticides, polybrominated biphenol ethers (PBDE), and polychlorinated biphenols (PCB) in salmon (Hites et al., 2004a, b; Montory and Barra, 2006; Hayward et al., 2007), PBDE and dioxin in catfish (Minh et al., 2006), dioxin and PCB in turbot (Blanco et al., 2007), PCB in sea bass (Carubelli et al., 2007) and PCB in all investigated fish (Pinto et al., 2008). Table 2 provides a summary of health risk associated with toxic contaminates that have been found in fish. For example, mercury contamination of fish was directly responsible for Minamata disease (a cerebral palsy-like disease) and has been linked with adverse neurocognitive outcomes in populations with high fish consumption (Davidson et al., 2006; Axelrad et al., 2007; EPA, 2001, 2004). Although mercury contamination levels are no higher in farmed fish than in wild fish (Easton et al., 2002; Hites et al., 2004a), their interactive toxic effects with co-existing man-made contaminants (as described earlier) are not known. Presumably, their consumption during pregnancy can raise health risk in the offspring, resulting in EPA guidance for fish limitations during pregnancy (Behrman et al., 2004;
Table 1. Contaminants found in studies of aquaculture fish vs. wild caught fish Contaminant
AC ¼ Wild
Mercury PAH Dioxin O.P. PCB PBDE Antibiotic
XX
AC4Wild
AC only
X XX XX XX XX X
X ¼ one study on contaminants of aquaculture vs. wild fish. XX ¼ two studies. AC ¼ aquacultured fish. PAH ¼ polyaromatic hydrocarbons. O.P. ¼ organophosphates. PBDE ¼ polybrominated diphenyl ethers. PCB ¼ polychlorinated biphenyl.
Table 2. exposure
Contaminates and known associated risks of
Contaminant
Associated risks
Mercury PBDE PCB Dioxin
Neuro-cognitive Cognitive/endocrine Cancer/cognitive Cancer hormonal/immune cardiovascular system Cancer/antibiotic resistance
Antibiotics
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PBDE ¼ polybrominated diphenyl ethers. PCB ¼ polychlorinated biphenyl.
Ford et al., 2001; EPA, 2004). PCBs have been linked to memory impairments, as well as other endocrine and cognitive abnormalities (Dewailly et al., 2007; Hites et al., 2004a; Foran et al., 2005). The finding of higher contaminant burden, especially from multiple man-made chemicals, in farmed compared to wild fish was surprising to consumers. From various estimates, consumption of these farmed fish can raise risk to health consequences such as cancer (Hites et al., 2004a, b; Foran et al., 2005; Hastein et al., 2006; Montory and Barra, 2006; Carubelli et al., 2007; Dewailly et al., 2007). Such health risk may overshadow the cardiovascular benefits from the consumption of certain farmed fish, especially for susceptible individuals such as pregnant or nursing women. Consequently, consumers should make informed decisions on the number of fish meals per week and on a mixture of wild and farmed fish. Efforts have been made to identify the source of such contaminations and to reduce the problem. It turns out that the contaminations have often been traced to the fish feeds because the contaminant levels in fish tissue have been correlated (and biomagnified) with that in the fish feed (Hites et al., 2004a, b; Blanco et al., 2007; Pinto et al., 2008). Another source is the inappropriate location of aquaculture at sites with high natural contaminants, e.g. arsenic in farmed tilapia (Ling et al., 2005; Jang et al., 2006). The obvious approach to reduce the first problem is to change and/or modify the fish feed. For example, selected removal of dioxin and PCB-like contaminants in fish feed can be made by employing partitioning and decontamination processes (Oterhals and Nygard, 2008). Alternatively, contaminant burden can be reduced by feeding fish with contaminant-free (and presumably more costly) feed towards the end of the aquaculture time, by taking advantage of the natural clearance of toxic chemicals and growth dilution character of the farmed fish (Brambilla et al., 2007). In addition, advisories can be provided to consumers to limit the consumption of certain fish, especially to susceptible people (EPA, 2004; Kiljunen et al., 2007).
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A contaminant in farmed fish that also attracted concern is antibiotic medication. Potentially maintaining the health of farmed fish for the short term, these antibiotics can be carcinogenic and may also lead to antibiotic resistance in human consumers (FDA Import Alert, 2007). The FDA recently banned the importation of 5 species of farmed fish from China in June 2007 following determination that 15% were contaminated with nitrofuran, malachite green, gentian violet, and/or fluoroquinolone antibiotics (FDA Press Conference, 2007; FDA Import Alert, 2007).
Regulations and international oversight of industry Regulations and international oversight for the aquaculture industry are extremely complex, with several agencies attempting to regulate site selection, pollution control, water quality, feed supply, production, and food safety (FAO, 2006, 2007a). These practices differ from country to country and sometimes between states and territories within a country. With the industry’s significant growth in the last twenty years and continued projected expansion, there are ongoing efforts to standardize practices across borders. In the US, there are as many as three departments, eleven federal agencies directly and another 10 indirectly involved in regulating aquaculture (DeVoe, 2007). The three US government departments are Agriculture (USDA), Commerce (DOC), and Interior (USDI). The USDA monitors and eradicates infected animals, and conducts research programs on vaccine development, genetic improvement, reproduction, nutrition, environmental compatibility, product safety, and quality (FAO, 2007a, b). The major responsibilities for DOC in aquaculture are: (1) minimization of environmental impacts and development of standards; (2) development of cost-effective, environmentally sound aquaculture and hatchery technology; (3) growth and production of marine species throughout their life cycle; (4) biotechnology to provide improved strains, sterile animals, detection of pathogens, and development of vaccines and other measures for controlling disease and parasites; (5) technology transfer to industry and government partners; and (6) coordination with management agencies to identify areas appropriate for aquaculture facilities and develop more efficient permitting procedures (FAO, 2007a, b). The USDI has two major programs: the Fish and Wildlife Service that operates the National Fish Hatchery System (NFHS) and the US Geological Survey. Their major responsibilities include fishery conservation, habitat preservation, reduction of disease
and improvement of health of aquatic organisms (FAO, 2007a, b). In order to ensure proper safety for imported aquaculture products and internal sale, the Hazard Analysis and Critical Control Points (HACCP) program has been implemented in the US and European Union (FAO, 2006). This program is also promoted by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO). FAO/WHO has published reports detailing recommendations on how different international markets can abide by the HACCP program. The HACCP program is a preventive approach to food safety. It focuses on physical, chemical, and biological hazards within the aquaculture process and implements actions, known as critical control points, to reduce or eliminate the hazard instead of only focusing on the finished product. ‘‘HACCP is based around seven established principles: (1) conduct a hazard analysis; (2) identify critical control points; (3) establish critical limits for each critical control point; (4) establish critical point monitoring requirements; (5) establish corrective actions; (6) establish record keeping procedures; and (7) establish procedures for ensuring the HACCP program is working as intended’’ (Goldberg et al., 2001). The HACCP system puts the responsibility of safe production and distribution of food products on the aquaculture sector. Major markets, such as North America and the European Union are requiring HACCP implementation (FAO, 2006). There is a strong international movement towards governments to adopt this program for their seafood-production sectors. This would provide the needed uniformity for aquaculture markets around the world to ensure the safe importation and exportation of its food products.
Conclusion and recommendations The many benefits of aquaculture provide a strong and credible argument for its continued implementation. For example, farmed fish provides high amount of omega-3 fatty acid that can benefit cardiovascular health of consumers at a much lower cost than wild fish (Mozzafarian and Rimm, 2006). On the other hand, the industry does have it own shares of problems and these are being addressed (FAO, 2007b). Aquaculture operations have been shown to have caused significant environmental degradation and the threats continue to be present. In addition, more attention needs to be paid to its unique occupational hazards. Infection of workers and natural species with organisms from farmed fish should be proactively prevented. Comprehensive occupational health and workplace safety programs need to be better organized and extended around the world.
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Such programs should address the effective application of primary prevention systems, personal protective measures, health surveillance, standardized regulatory guidelines, and sound management practices. It was a surprise to consumers that farmed fish can have higher concentrations of certain toxic chemicals, especially man-made chemicals, than wild fish. The main sources of contamination are from bioaccumulation via fish feed and from location of aquaculture in contaminated areas. The former problems can potentially be minimized by changing the fish feed and by advisories on limiting the consumption of farmed fish, especially for susceptible individuals such as pregnant or nursing women. The continued growth and diversification of the aquaculture industry requires increasing numbers of governmental policies and recommendations. The most current policy, the HACCP which has been adapted by the US and the European Union, puts the responsibility of safe production and distribution of food products on the aquaculture sector (FAO, 2006, 2007a, b). This system would provide the needed uniformity for aquaculture markets around the world to ensure the safe importation and exportation of its food products. Aquaculture continues to provide valuable food supply and economic support for many countries. At the same time, we must remind ourselves that even though aquaculture provides many benefits, we must strive to preserve the environment we inhabit, and continue to provide a safe and reliable source of food that can also enhance the health of millions of people globally.
Acknowledgement This review is the product of a project resulting from an Environmental Health and Toxicology Course in the Master of Public Health program at the University of Texas Medical Branch (UTMB) in Galveston, Texas, USA. David W. Cole, M.D., Steven J. Gaydos, M.D., Jon Gray, M.D., Mark L. Jacques, M.D., Nicole Powell-Dunford, M.D. are in the Army Aerospace Medicine Residency program; Greg Hyland, M.D. is in the Air Force Aerospace Medicine Residency program; Richard W. Cole is in the UTMB Aerospace Medicine Residency Program; and Charu Sawhney, D.O. is in the UTMB General Preventive Medicine Residency Program. Disclaimer: The views, opinions, and/or citations in this report are those of the authors and should not be construed as official Department of the Army, Department of the Air Force, or the Department of Defense position, policy or decision, unless so designated by other official documentations.
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Aquaculture: Environmental, toxicological, and health issues David W. Cole, Richard Cole, Steven J. Gaydos, Jon Gray, Greg Hyland, Mark L. Jacques, Nicole Powell-Dunford, Charu Sawhney, William W. Au Department of Preventive Medicine and Community Health, 700 Harborside Drive, University of Texas Medical Branch, Galveston, TX 77555-1110, USA Received 26 February 2008; received in revised form 10 July 2008; accepted 15 August 2008
Abstract Aquaculture is one of the fastest growing food-producing sectors, supplying approximately 40% of the world’s fish food. Besides such benefit to the society, the industry does have its problems. There are occupational hazards and safety concerns in the aquaculture industry. Some practices have caused environmental degradation. Public perception to farmed fish is that they are ‘‘cleaner’’ than comparable wild fish. However, some farmed fish have much higher body burden of natural and man-made toxic substances, e.g. antibiotics, pesticides, and persistent organic pollutants, than wild fish. These contaminants in fish can pose health concerns to unsuspecting consumers, in particular pregnant or nursing women. Regulations and international oversight for the aquaculture industry are extremely complex, with several agencies regulating aquaculture practices, including site selection, pollution control, water quality, feed supply, and food safety. Since the toxicological, environmental, and health concerns of aquaculture have not been adequately reviewed recently, we are providing an updated review of the topic. Specifically, concerns and recommendations for improving the aquaculture industry, and for protection of the environment and the consumers will be concisely presented. r 2008 Elsevier GmbH. All rights reserved. Keywords: Aquaculture; Fish; Nutrition; Occupational health; Pesticides; Public health
Introduction Husbandry of aquatic organisms has been practiced through the ages (Bardach et al., 1972). Oyster culture, for instance, thrived in ancient Rome and Gaul (Bardach et al., 1972). Humankind has always been in search of more efficient food-production methods for ever increasing human consumption. In addition, many fish are produced in hatcheries for sport fishing and repletion of wild stock, such as trout, largemouth bass, Corresponding author. Tel.: +1 409 772 1545; fax: +1 409 772 9108. E-mail address: [email protected] (W.W. Au).
1438-4639/$ - see front matter r 2008 Elsevier GmbH. All rights reserved. doi:10.1016/j.ijheh.2008.08.003
and salmon. Thus, one would recognize that aquaculture not only feeds the human population, but also provides a vital service to replenish certain species. Since the 1960s, aquaculture production have increased dramatically due to much improved conditions such as water quality, disease control, nutritionally complete feeds, and the development of improved stocks through selective breeding, hybridization, and the application of molecular genetics technology (Stickney, 1994). Globally, farmed fish production more than doubled from 1987 to 1997 at a rate of 9% per year (Englehaupt, 2007) and aquaculture is becoming a major industry that provides approximately 43% of seafood to the consumers (FAO, 2006, 2007a). China
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remains the largest producer with reported fisheries production of 47.5 million tons in 2004 providing an estimated domestic food supply of 28.4 kg per capita as well as production for export and non-food purposes, followed by India and the Philippines (FAO, 2006). The United States (US) ranks third in the world in consumption of seafood and eleventh in the world in aquaculture production, therefore the US has historically had to rely on high levels of seafood imports (Goldberg et al., 2001). It may appear that aquaculture is highly beneficial and has no drawbacks but that is far from accurate. The aquaculture industry, like other industries, has its share of occupational hazards, safety concerns, and risks to the individual health of the worker. There also exist several deleterious effects on the environment from aquaculture. Farmed fish, although presumably safer from contamination than wild fish, have, in fact, higher body burden of certain toxic chemicals that may present health concerns to unsuspecting consumers. On the other hand, a major benefit of farmed fish is that they provide a good and low-cost source of polyunsaturated fatty acids (PUFA’s) which can enhance cardiovascular health in humans. Regulations and international oversight for the aquaculture industry are extremely complex, with several agencies attempting to regulate aquaculture practices, including site selection, pollution control, water quality, feed supply, and food safety. These practices differ from country to country and sometimes between states and territories within a country. However, there are ongoing efforts to standardize practices across borders and harmonize international regulations. The concerns and recommendations for improving the aquaculture industry are of constant interest. From our literature search in PubMed, we recognized that there are only a handful of review papers on the general topic during the last two years. The majority of them, however, focused on infection and microbiological problems. Therefore, an updated review of environmental, toxicological and health concerns of aquaculture is needed. Our current review has also included recent publications on the topic.
Genetic manipulation in aquaculture and the ecological impact on the environment The use of technologies and breeding programs has generated aquaculture species that are both more practical and economical to produce. For example, male tilapia grows faster than females, making it the preferred sex for commercial production. A YY male genotype sires progeny that are nearly all males (Muir, 2005). In contrast, rainbow trout are selected for an all
female crop for better growth rate and less risk of precocious maturity (Muir, 2005). Gynogenesis inbreeds these female fish by using irradiated sperm so the progeny have no paternal genes making an all female generation (Halvorson and Quezada, 1999). Atlantic salmon raised in British Colombia are sterile triploid females to prevent their breeding with wild Pacific salmon in the event of an escape (Hulata, 2001; Reichhardt, 2000). Salmons are sterilized by heating or providing a pressure shock to the eggs shortly after fertilization to retain an extra set of chromosomes (Reichhardt, 2000). Further sex-control technologies include endocrine treatments for sex reversal (Hulata, 2001). Potential environmental and genetic hazards exist if modified fish are released into the wild, e.g. unintentionally as a result of escape (Stokstad, 2002; MauryBrachet et al., 2008). These fish that are then introduced into the wild may spread unique diseases and parasites (Beveridge, 1990). An example is a recent report indicating that sea lice from farmed salmon can possibly cause certain native salmons in British Columbia to plummet by 99% within eight years (Krkosek et al., 2007). The ecological impacts are also centered on heightened predation and altered population or ecosystem secondary to the escaped fish’s activities (Goldberg et al., 2001). The modified fish may become established where that species was not previously present. For instance, a fish genetically altered with antifreeze protein could migrate ‘‘upstream’’ to a colder environment where the wild species cannot survive and displace the endogenous species. The genetically altered fish could reproduce with the feral type resulting either in a more robust fish that disrupts the environment or in poorly fit fish causing a gradual extinction of the species (Goldberg et al., 2001). The development of beneficial transgenic organisms requires the insertion of appropriate genes during the blastocyst stage of embryonic development. Genes that can provide highly desirable benefits include: growth hormone, freeze protection and disease resistant genes (Halvorson and Quezada, 1999). Transgenic fish have been produced in Atlantic salmon, Coho salmon, Chinook salmon, rainbow trout, cutthroat trout, tilapia, striped bass, channel catfish, common carp, and Indian major carps (FAO, 2007b). For example, Aqua Bounty Farms Inc., of Waltham Massachusetts has developed a transgenic Atlantic salmon that can grow up to six times as fast as ordinary farm-raised salmon after the introducing of a growth hormone and promoter sequences from a Chinook salmon (Stokstad, 2002). Although commercial production of transgenic fish has been seriously considered (Hu et al., 2007), transgenic fish has not been approved by the US Food and Drug Administration for human consumption yet (Muir and
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Howard, 1999; FAO, 2007b; Hallerman, Personal communication).
Occupational hazards of aquaculture The occupational hazards, safety concerns, and risks to health in the aquaculture industry can vary considerably based on the types of operation, scale of production, and even the specific species of interest (EFSA, 2005). In 2006, the non-fatal occupational injury incidence rate for aquaculture (injuries per 100 full-time workers) was 6.8 (Survey of Occupational Injuries and Illnesses, Bureau of Labor Statistics, USA). In comparison, terrestrial crop production was 5.3 and animal production was 7.8. Aquaculture occupational hazards and risks to health can generally be categorized into those concerning physical work hazards, chemical and toxic exposures, and risks associated with infectious disease. Regarding the physical work environment, risks concerning machinery and tool use are similar to that of terrestrial agriculture. High-torque capacity tractors used in aquaculture, for example, are subject to the same roll-over protection (Occupational Safety and Health Administration (OSHA) compliance standards) as farm tractors (OSHA, 2007). Electrocution and high-voltage electrical accidents are also of concern, particularly due to the proximity of water (Durborow, 1999). Other hazards might include drowning, musculoskeletal injuries from repetitive lifting of heavy cages and nets, over-use injuries like tenosynovitis from repetitive motion tasks, and long-term exposure in extreme environments of sunlight, wind, cold, and water (Douglas, 1995). Therefore, personal flotation devices (PFDs), thermal protection for cold environment and foam-padded PFDs against chest and rib injuries are needed (Douglas, 1995). Divers are also at risk for decompression sickness. Such cases have been reported with multiple descents and ascents (deemed ‘‘yo-yo’’ diving) to clear dead fish from cages, even in relatively shallow water of less than 20 m (Douglas, 1991). Toxic exposures are of concern to aquaculture workers because they can be exposed to unique and toxic chemicals, e.g. Nessler’s Reagent which is used to test for the presence of ammonia contains potassium hydroxide, mercuric iodide, and potassium iodide (Durborow, 1999). Hydrogen sulfide (H2S) occurs naturally from organic breakdown, often during anaerobic reactions on pond bottoms (Durborow, 1999). H2S can cause anoxic brain injury and unconsciousness at high levels and is predominantly a mucous membrane and respiratory irritant at lower levels (Kuschner and Blanc, 2007). In one unfortunate case, the autopsies of three drowned aquaculture workers reveled sublethal
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H2S levels, and this exposure was thought to have contributed to their drownings (Durborow, 1999). Toxicity information on products is typically focused on single chemicals. In aquaculture, combining the use of multiple toxic products can be a common practice. Such practices can produce toxic by-products and harmful gases from chemical reactions, and the health risk to workers under this condition is not known. There are health risks to workers associated with microbial exposure and processes related to the prevention of infectious diseases in aquaculture species. For example, with respect to prevention, accidental autoinoculation or self-injection with antimicrobials, immunizations, or veterinary biologics carries the potential to produce a range of pathology in the worker from local tissue reaction to full anaphylaxis (Douglas, 1995; Durborow, 1999). Aquaculture workers can be exposed to uncommon microbes including bacteria, viruses, algae, and parasites potentially causing zoonotic disease or emerging infections. For example, four separate tilapia fish processors developed health complications subsequent to infection with Streptococcus iniae, a fish pathogen not previously reported to be a cause of disease in humans (CDC, 1996; Garrett et al., 1997). As published by Durborow (1999), many other fish pathogens are known to be contagious to humans, including several species of the genera Mycobacterium and Vibrio (especially M. marinum, V. vulnificus, and V. parahemolyticus), as well as species of Streptococcus, Aeromonas, Erysipelothrix, and Pseudomonas. A more inclusive list would also include parasites (nematodes, trematodes, and flukes), protozoans, and dinoflagellates.
Environmental impact from aquaculture Environmental degradation from aquaculture practices has been reported. The negative effects include organic pollution and eutrophication, a buildup of excess nutrients (primarily organic nitrogen and phosphorus) and wastes in an ecosystem. These problems together with chemical pollution can cause algal bloom, depletion of oxygen, reduction in water quality, death of corals and habitat destruction (Boesch et al., 2001; Aubin, 2006). Certain microorganisms that thrive in this adverse environment are directly harmful to fish through biologic and neurologic toxins (Aubin, 2006). These detrimental effects are usually localized to surrounding regions and can be transitory. Therefore, good management protocols can be used to minimize the effects, e.g. situate net pens in areas with high natural flushing rates, periodic fallowing between cycles of production, use of seaweed biofilters and use of mollusk-farming to remove organic nitrogen from the water (Kaspar et al., 1985; Chopin et al., 1999; Debruyn et al., 2006).
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A large quantity of wild-caught fish has been used as feeds for aquaculture. However, when these forage fish stocks are heavily harvested, it can directly affect marine ecosystems negatively by the reduction of food available for predators (Naylor et al., 2000). Therefore, alternative sources of feed are being considered. Chemicals used in aquaculture can also cause pollution in the environment. These chemicals can come from antibiotics, pesticides, herbicides, hormones, anesthetics, pigments, minerals, and vitamins (Goldberg et al., 2001; JSA, 2007). There is limited data on the extent of antibiotic use by producers outside of the USA but they may rely on antibiotics to a greater extent (Mellon et al., 2001). A concern about antibiotic use is that it may affect un-intended species leading to antibiotic resistance and other toxic effects (Brown, 1989). This may have been a reason why some pathogens have become resistant to many drugs that are used in aquaculture (Dixon, 2000). Herbicides are used to control aquatic weeds, algal blooms, and fouling organisms. Net pen operators often treat their nets with paints that contain copper-based algaecide. These and other compounds appear relatively safe when applied in approved conditions; however, there are concerns that a spill of these chemicals can cause irreversible damage to the environment (Eisler, 1998). Diseases and parasites for aquaculture can be deleterious in wild fish stock. Parasites may serve as a host for other lethal diseases such as infectious salmon anemia (ISA) which has been detected in both escaped farmed and wild fish (FWS/NOAA, 2000). Another example of parasite introductions into the environment is sea lice which is a serious problem affecting salmon farms and can also impact wild salmon migrating through coastal waters (Finstad et al., 2000; Krkosek et al., 2007). A concern that attracts a lot of attention is the alteration and destruction of natural habitats. Habitat modification is an important aspect for increasing aquaculture productivity. It includes direct habitat conversion and predator-control programs (Goldberg et al., 2001). In some areas, flow and composition of rivers is altered because of the biological processes of non-native species. Farmed species may feed on and cause local extinction of certain plant and aquatic species. Clustering or poor sitting of aquaculture operations can also obstruct wild animals’ use of their natural surroundings including the passage of migrating fish (Goldberg et al., 2001). Other organisms may be introduced or removed from areas of aquaculture therefore transforming the environment food web and overall cycle (Phillips, 1990). Aquaculture has some environmentally positive effects as well. Aquaculture can reduce the dependence on natural stocks as well as genetic conservation of endangered species. Aquaculture is also useful in areas
of limited aquatic life, by enrichment of the local water column. Aquaculture indirectly benefits the environmental by providing a method to convert agriculture waste into high-quality fish protein, by enriching pond mud for use as fertilizer and for improving soil quality on crop land (Muir, 1999).
Nutritional value and comparison with wild seafood Fish muscle is an abundant source of PUFA’s in the human diet, especially n-3 and n-6, or more commonly known as omega-3 and omega-6, fatty acids. It is believed that two of the very long-chain omega-3 fatty acids, eicosapentaenoic acid, and docosahexaenoic acid, specifically may lower the risk of coronary heart disease in humans (van Vliet and Katan, 1990). Fish is the major dietary source of these two important fatty acids in humans. Therefore, the American Heart Association (AHA) recommends that healthy adults eat at least two servings of fish per week. The AHA also recommends that individuals with coronary heart disease need 1 g of combined eicosapentaenoic acid and docosahexaenoic acid per day; while those who have elevated triglycerides may need 2–4 g per day (AHA, 2007). Such benefit from fish consumption makes comparing the composition of these fatty acids in fish muscle between wild and farmed fish an important investigation. Among trout, salmon and sea bass, higher levels of beneficial omega-3 to omega-6 fatty acid ratios were found in farmed compared to wild fish (Suzuki et al., 1986; van Vliet and Katan, 1990; Alasalvar et al., 2002). In addition, the beneficial fatty acid composition of farmed fish can be increased through the manipulation of their diet (Bell et al., 2001). For example, Alasalvar et al. (2002) showed that feeding fish with feed that contained higher levels monoenoic acids led to higher levels of these fatty acids in fish tissues. Similar observations were made with oleic acids (Alasalvar et al., 2002). More recently, fish feeds have also included the use of vegetable sources such as soybeans, rapeseed, and wheat (Cahu et al., 2004). The benefits and limitations on nutritional values from the use of the modified fish feed needs to be evaluated. Another topic which has been scientifically studied is the area of trace mineral and vitamin contents in fish. Nettleton and Exler (1992) reported that, among finfish, the only difference across all species was greater niacin content in raw samples of farmed versus wild trout. This difference, however, was not seen among the corresponding cooked samples of trout. Alasalvar et al. (2002) examined several essential and non-essential minerals in fish samples and found higher levels of Fe,
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Al, Ti, and V in wild sea bass compared to their farmed counterparts.
Contamination in fish and health issues Consumers may select farmed fish for meal as a healthier and safer alternative to wild fish because aquaculture is presumably located away from industries that generate contaminated air and water. However, consumers have been surprised to find that several natural and man-made toxic substances are at higher concentrations in farmed than wild fish (Table 1). Some examples of man-made contaminants in farmed fish are: pesticides, polybrominated biphenol ethers (PBDE), and polychlorinated biphenols (PCB) in salmon (Hites et al., 2004a, b; Montory and Barra, 2006; Hayward et al., 2007), PBDE and dioxin in catfish (Minh et al., 2006), dioxin and PCB in turbot (Blanco et al., 2007), PCB in sea bass (Carubelli et al., 2007) and PCB in all investigated fish (Pinto et al., 2008). Table 2 provides a summary of health risk associated with toxic contaminates that have been found in fish. For example, mercury contamination of fish was directly responsible for Minamata disease (a cerebral palsy-like disease) and has been linked with adverse neurocognitive outcomes in populations with high fish consumption (Davidson et al., 2006; Axelrad et al., 2007; EPA, 2001, 2004). Although mercury contamination levels are no higher in farmed fish than in wild fish (Easton et al., 2002; Hites et al., 2004a), their interactive toxic effects with co-existing man-made contaminants (as described earlier) are not known. Presumably, their consumption during pregnancy can raise health risk in the offspring, resulting in EPA guidance for fish limitations during pregnancy (Behrman et al., 2004;
Table 1. Contaminants found in studies of aquaculture fish vs. wild caught fish Contaminant
AC ¼ Wild
Mercury PAH Dioxin O.P. PCB PBDE Antibiotic
XX
AC4Wild
AC only
X XX XX XX XX X
X ¼ one study on contaminants of aquaculture vs. wild fish. XX ¼ two studies. AC ¼ aquacultured fish. PAH ¼ polyaromatic hydrocarbons. O.P. ¼ organophosphates. PBDE ¼ polybrominated diphenyl ethers. PCB ¼ polychlorinated biphenyl.
Table 2. exposure
Contaminates and known associated risks of
Contaminant
Associated risks
Mercury PBDE PCB Dioxin
Neuro-cognitive Cognitive/endocrine Cancer/cognitive Cancer hormonal/immune cardiovascular system Cancer/antibiotic resistance
Antibiotics
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PBDE ¼ polybrominated diphenyl ethers. PCB ¼ polychlorinated biphenyl.
Ford et al., 2001; EPA, 2004). PCBs have been linked to memory impairments, as well as other endocrine and cognitive abnormalities (Dewailly et al., 2007; Hites et al., 2004a; Foran et al., 2005). The finding of higher contaminant burden, especially from multiple man-made chemicals, in farmed compared to wild fish was surprising to consumers. From various estimates, consumption of these farmed fish can raise risk to health consequences such as cancer (Hites et al., 2004a, b; Foran et al., 2005; Hastein et al., 2006; Montory and Barra, 2006; Carubelli et al., 2007; Dewailly et al., 2007). Such health risk may overshadow the cardiovascular benefits from the consumption of certain farmed fish, especially for susceptible individuals such as pregnant or nursing women. Consequently, consumers should make informed decisions on the number of fish meals per week and on a mixture of wild and farmed fish. Efforts have been made to identify the source of such contaminations and to reduce the problem. It turns out that the contaminations have often been traced to the fish feeds because the contaminant levels in fish tissue have been correlated (and biomagnified) with that in the fish feed (Hites et al., 2004a, b; Blanco et al., 2007; Pinto et al., 2008). Another source is the inappropriate location of aquaculture at sites with high natural contaminants, e.g. arsenic in farmed tilapia (Ling et al., 2005; Jang et al., 2006). The obvious approach to reduce the first problem is to change and/or modify the fish feed. For example, selected removal of dioxin and PCB-like contaminants in fish feed can be made by employing partitioning and decontamination processes (Oterhals and Nygard, 2008). Alternatively, contaminant burden can be reduced by feeding fish with contaminant-free (and presumably more costly) feed towards the end of the aquaculture time, by taking advantage of the natural clearance of toxic chemicals and growth dilution character of the farmed fish (Brambilla et al., 2007). In addition, advisories can be provided to consumers to limit the consumption of certain fish, especially to susceptible people (EPA, 2004; Kiljunen et al., 2007).
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A contaminant in farmed fish that also attracted concern is antibiotic medication. Potentially maintaining the health of farmed fish for the short term, these antibiotics can be carcinogenic and may also lead to antibiotic resistance in human consumers (FDA Import Alert, 2007). The FDA recently banned the importation of 5 species of farmed fish from China in June 2007 following determination that 15% were contaminated with nitrofuran, malachite green, gentian violet, and/or fluoroquinolone antibiotics (FDA Press Conference, 2007; FDA Import Alert, 2007).
Regulations and international oversight of industry Regulations and international oversight for the aquaculture industry are extremely complex, with several agencies attempting to regulate site selection, pollution control, water quality, feed supply, production, and food safety (FAO, 2006, 2007a). These practices differ from country to country and sometimes between states and territories within a country. With the industry’s significant growth in the last twenty years and continued projected expansion, there are ongoing efforts to standardize practices across borders. In the US, there are as many as three departments, eleven federal agencies directly and another 10 indirectly involved in regulating aquaculture (DeVoe, 2007). The three US government departments are Agriculture (USDA), Commerce (DOC), and Interior (USDI). The USDA monitors and eradicates infected animals, and conducts research programs on vaccine development, genetic improvement, reproduction, nutrition, environmental compatibility, product safety, and quality (FAO, 2007a, b). The major responsibilities for DOC in aquaculture are: (1) minimization of environmental impacts and development of standards; (2) development of cost-effective, environmentally sound aquaculture and hatchery technology; (3) growth and production of marine species throughout their life cycle; (4) biotechnology to provide improved strains, sterile animals, detection of pathogens, and development of vaccines and other measures for controlling disease and parasites; (5) technology transfer to industry and government partners; and (6) coordination with management agencies to identify areas appropriate for aquaculture facilities and develop more efficient permitting procedures (FAO, 2007a, b). The USDI has two major programs: the Fish and Wildlife Service that operates the National Fish Hatchery System (NFHS) and the US Geological Survey. Their major responsibilities include fishery conservation, habitat preservation, reduction of disease
and improvement of health of aquatic organisms (FAO, 2007a, b). In order to ensure proper safety for imported aquaculture products and internal sale, the Hazard Analysis and Critical Control Points (HACCP) program has been implemented in the US and European Union (FAO, 2006). This program is also promoted by the Food and Agriculture Organization of the United Nations (FAO) and the World Health Organization (WHO). FAO/WHO has published reports detailing recommendations on how different international markets can abide by the HACCP program. The HACCP program is a preventive approach to food safety. It focuses on physical, chemical, and biological hazards within the aquaculture process and implements actions, known as critical control points, to reduce or eliminate the hazard instead of only focusing on the finished product. ‘‘HACCP is based around seven established principles: (1) conduct a hazard analysis; (2) identify critical control points; (3) establish critical limits for each critical control point; (4) establish critical point monitoring requirements; (5) establish corrective actions; (6) establish record keeping procedures; and (7) establish procedures for ensuring the HACCP program is working as intended’’ (Goldberg et al., 2001). The HACCP system puts the responsibility of safe production and distribution of food products on the aquaculture sector. Major markets, such as North America and the European Union are requiring HACCP implementation (FAO, 2006). There is a strong international movement towards governments to adopt this program for their seafood-production sectors. This would provide the needed uniformity for aquaculture markets around the world to ensure the safe importation and exportation of its food products.
Conclusion and recommendations The many benefits of aquaculture provide a strong and credible argument for its continued implementation. For example, farmed fish provides high amount of omega-3 fatty acid that can benefit cardiovascular health of consumers at a much lower cost than wild fish (Mozzafarian and Rimm, 2006). On the other hand, the industry does have it own shares of problems and these are being addressed (FAO, 2007b). Aquaculture operations have been shown to have caused significant environmental degradation and the threats continue to be present. In addition, more attention needs to be paid to its unique occupational hazards. Infection of workers and natural species with organisms from farmed fish should be proactively prevented. Comprehensive occupational health and workplace safety programs need to be better organized and extended around the world.
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Such programs should address the effective application of primary prevention systems, personal protective measures, health surveillance, standardized regulatory guidelines, and sound management practices. It was a surprise to consumers that farmed fish can have higher concentrations of certain toxic chemicals, especially man-made chemicals, than wild fish. The main sources of contamination are from bioaccumulation via fish feed and from location of aquaculture in contaminated areas. The former problems can potentially be minimized by changing the fish feed and by advisories on limiting the consumption of farmed fish, especially for susceptible individuals such as pregnant or nursing women. The continued growth and diversification of the aquaculture industry requires increasing numbers of governmental policies and recommendations. The most current policy, the HACCP which has been adapted by the US and the European Union, puts the responsibility of safe production and distribution of food products on the aquaculture sector (FAO, 2006, 2007a, b). This system would provide the needed uniformity for aquaculture markets around the world to ensure the safe importation and exportation of its food products. Aquaculture continues to provide valuable food supply and economic support for many countries. At the same time, we must remind ourselves that even though aquaculture provides many benefits, we must strive to preserve the environment we inhabit, and continue to provide a safe and reliable source of food that can also enhance the health of millions of people globally.
Acknowledgement This review is the product of a project resulting from an Environmental Health and Toxicology Course in the Master of Public Health program at the University of Texas Medical Branch (UTMB) in Galveston, Texas, USA. David W. Cole, M.D., Steven J. Gaydos, M.D., Jon Gray, M.D., Mark L. Jacques, M.D., Nicole Powell-Dunford, M.D. are in the Army Aerospace Medicine Residency program; Greg Hyland, M.D. is in the Air Force Aerospace Medicine Residency program; Richard W. Cole is in the UTMB Aerospace Medicine Residency Program; and Charu Sawhney, D.O. is in the UTMB General Preventive Medicine Residency Program. Disclaimer: The views, opinions, and/or citations in this report are those of the authors and should not be construed as official Department of the Army, Department of the Air Force, or the Department of Defense position, policy or decision, unless so designated by other official documentations.
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