2.5 Safety of Food Products from Aquaculture

As aquaculture assumes an expanding role in meeting consumer demand for fishery products, it is only natural that the quality and safety of its products come under the scrutiny of national and international organizations responsible for food safety. The issue of safety and quality is of concern to all consumers in both producing and importing countries, and hints of potential hazard may be sufficient, under some circumstances, to create economic damage. Recent concern about assessment and control of food safety and quality in aquaculture is both timely and important, as is the development of an information base and other tools to enable objective assessment of hazards and risks.

The 1995 FAO Conference adopted the Code of Conduct for Responsible Fisheries which calls for, inter alia, food safety and quality of aquaculture products. The Code’s Article 9 Aquaculture Development, and in particular its provisions for Responsible Aquaculture at the Production Level, address the need for safe and effective use of feeds, feed additives, fertilizers, manure, chemo-therapeutants and other chemicals.

The rules that govern international trade in food were agreed upon during the Uruguay-Round on Multilateral Trade Negotiations and apply to all members of the World Trade Organization (WTO). With regard to food safety, these rules are set out in the Agreement on Sanitary and Phytosanitary Measures (SPS Agreement). According to the SPS Agreement, WTO members have the right to take legitimate measures to protect the life and health of their people from hazards in food, but these measures may not be unjustifiably trade restrictive. Also, these measures have to be based on risk assessment, taking into consideration the risk assessment techniques developed by relevant international organizations. In regard to food safety, the relevant international organization is the FAO/WHO Codex Alimentarius Commission (CAC)². In order to facilitate and harmonize risk assessment, the CAC has adopted a number of definitions in relation to risk analysis. In this context, it is particularly important to recognize that a hazard is a biological, chemical or physical agent in, or condition of, food, with the potential to cause harm. In contrast, risk is an estimate of the probability and severity of adverse health effects in exposed populations, consequential to hazard(s) in food.

Identification of hazards in food and the determination of their relevance for health as well as their control is the function of the science of risk analysis. Risk analysis is an emerging discipline in food control; the methodological basis for assessing, managing and communicating risks associated with food-borne hazards is, at the international level, still in a developing phase.

Within the Codex system, broad issues relating to food safety that are also applicable to products from aquaculture, fall under the general subject committees, such as the Codex Committees on Food Additives and Contaminants, Food Hygiene, Pesticide Residues, and Residues of Veterinary Drugs in Foods. The Codex Committee on Food Hygiene has revised the International Code of Practice on General Principles of Food Hygiene which lays a firm foundation for ensuring food hygiene throughout the food chain, from primary production through to final consumption. It recommends a HACCP-based approach (see below) wherever possible to enhance food safety, and the controls described are internationally recognized as essential to ensure the safety and suitability of food for consumption. In addition, specific food safety issues are covered by the Codex Committee on Fish and Fishery Products, which is preparing the Draft Code of Hygienic Practice for the Products of Aquaculture (FAO, 1996). This draft code is under revision and it is intended to assist those engaged in aquaculture to produce high-quality fish that is safe for human consumption. The Code covers all stages of the aquaculture production cycle, from the selection of a site for establishing a fish farm, to grow out and primary on-farm handling of products.

A number of meetings have been convened as part of the effort to develop risk analysis for food safety at the international level, to synthesize and disseminate information on food safety (including food production from aquaculture), and to address related issues. These have included:

• FAO/WHO Consultation on HACCP: Concept and Application (WHO, 1995a);
• FAO/WHO Expert Consultation on the Application of Risk Analysis to Food Standard Issues (WHO, 1995b);
• FAO/WHO Expert Meeting on Food Safety Risk Management (FAO, 1997);
• FAO Expert Consultation on Animal Feeding and Food Safety (FAO, in press).

Meetings focused exclusively on aquaculture have included the SEAFDEC³/FAO/CIDA⁴ Expert Meeting on the Use of Chemicals in Aquaculture in Asia (SEAFDEC/FAO/CIDA, in press), the findings of which were discussed by an ad hoc meeting of the GESAMP⁵ Working Group on Environmental Impacts of Coastal Aquaculture (GESAMP, 1997); and a Joint FAO/NACA⁶/WHO Study Group on Food Safety Issues Associated with Products from Aquaculture (WHO, in press). The Study Group considered food safety issues associated with farmed finfish and crustaceans, particularly those associated with biological and chemical contamination that may occur during the production of these aquatic products. It considered the quantification of hazards and how to implement measures for control of potential food safety hazards, including current national and international programmes. It also identified knowledge gaps and research needs (WHO, in press).

Hazards and risks that may adversely affect the health of people are inherent in all human activities. Aquaculture is no exception to this general rule. Unfortunately, whereas 87% of the world production from aquaculture derives from developing countries in the tropics and sub-tropics, most of the literature on hazards and the public health aspects of fish and fishery products deals predominantly with the hazards of marine fish caught or harvested in temperate waters, and processed and marketed in developed countries (Ward, 1989; Liston, 1990; Ahmed, 1991a; Ahmed, 1991b; Gibson, 1992). Information on hazards associated with aquaculture species from warm waters is sparse in comparison (Edwards, 1992; Reilly, 1992; Buras, 1993). An exhaustive review of the safety of food products from aquaculture is not in the remit of this article. However, some major issues are summarized below.

Food-borne trematode infections, food-borne diseases associated with pathogenic bacteria and viruses, residues of agro-chemicals, veterinary drugs and heavy-metal organic or inorganic contamination have been identified as possible hazards in aquaculture products (Garrett et al., 1997; Reilly et al., 1997). These hazards are usually associated with the aquaculture habitat, the species being farmed, the general condition of the local environment, and cultural habits of food preparation and consumption. Fortunately, one of the several advantages of aquaculture as a source of food fish is that the producer can exert control over the intrinsic quality, including the safety, of the product. Though this aspect of aquaculture may not have received adequate attention until very recently, many of the identified potential hazards at the production level can be controlled by good fish farm management practices, and consumer education regarding such risks as eating raw or partially cooked products that may contain parasites. The introduction of safety management systems in fish farm management may add to the cost of aquatic products. However, the added cost will probably be small and there could be, in fact, a cost saving--the management controls and improved quality assurance can result in improved efficiency of production and reduction of cost. Furthermore, the cost of placing unsafe food products on the market can be detrimental to the industry as well as to national economies in terms of product rejection in international trade and industry reputation (Reilly et al., 1997).

The principal biological agents that cause food-borne disease are bacteria, viruses, parasites and to a lesser extent, moulds. Parasite-related food safety concerns in aquaculture are limited to a few helminth species, and the hazards are largely focused on communities where consumption of raw or inadequately cooked fish is a cultural habit (WHO, 1995c; WHO, in press). The main human diseases caused by fish-borne parasites are trematodiasis, cestodiasis, and nematodiasis. Trematodes are by far the most important food safety hazard linked with fish and fishery products. These parasites can cause illnesses ranging from debilitation to cancers and death. The most important trematodes, so far as numbers of people affected is concerned, are species of the genera Clonorchis, Opisthorchis and Paragonimus. WHO (1995) estimates that tens of millions of people are affected by fish-borne trematodes, though not necessarily of aquaculture origin. There is a lack of specific and quantitative information about the extent of the hazard in farmed fish, but the little information we have shows that parasites are found in farmed fish, and there is some, though scanty, epidemiological evidence of transmission of trematode parasites from farmed fish. Since a large volume of global production of farmed freshwater fish is produced in areas of the world where these parasites are endemic in the natural fish population, and are the cause of considerable illness to humans, it can be assumed from a precautionary viewpoint that freshwater fish farmed in these areas pose a potential hazard, even if the risk cannot be objectively assessed at this time.

Molluscs present a higher risk of causing human illness from bacterial or viral pathogens than do crustaceans and finfish. The greatest number of seafood-associated illnesses are from consumption of raw molluscs harvested in waters contaminated with raw or poorly treated human sewage (Ahmed, 1991a; Hackney and Pierson, 1994). However, there is no indication that mollusc farming practices per se increase the risk over that of bivalves harvested from wild populations from the same waters (Hackney and Pierson, 1994). Human viral diseases caused by the consumption of finfish and crustaceans appear to present a low risk, while viruses causing disease in fish are not pathogenic to man.

The level of contamination of aquaculture products by pathogenic bacteria will depend on the environment and the bacteriological quality of the water where the fish is cultured. There are two broad groups of bacteria of public health significance that will contaminate products of aquaculture: those naturally present in the environment--indigenous microflora (e.g. Aeromonas hydrophila, Clostridium botulinum, Vibrio parahaemolyticus, Vibrio cholerae, Vibrio vulnificus, and Listeria monocytogenesi); and those introduced through environmental contamination by domestic animal excreta and/or human wastes--non-indigenous microflora (e.g. Enterobacteriacae such as Salmonella spp., Shigella spp., and Escherichia coli) (Huss, 1994).

It should be noted that non-indigenous bacteria of faecal origin can be introduced into aquaculture ponds via unavoidable contamination by birds and terrestrial animals associated with farm waters, in systems in which manures are not used for nutritional input. There is a rapid die-off of enteric organisms and viruses in well managed ponds (Edwards, 1992; Buras, 1993), but significant numbers of organisms remain on the skin and in the guts of fish and can pose a health risk to consumers. Therefore, regulatory authorities should not immediately assume that raw aquaculture products, particularly raw frozen shrimp, containing Salmonella are due to poor sanitary practices. Adequate cooking (i.e. the thermal centre of the product should reach 70°C) before consumption will eliminate the risk. Epidemiological evidence suggests that a far higher level of consumer risk from these bacteria is associated with eating other products of animal origin, such as poultry and red meats, than with eating finfish and crustaceans from culture or capture fisheries (WHO, in press).

Cholera (Vibrio cholerae) and gastroenteritis (e.g. V. parahaemolyticus) have been associated with consumption of raw fish and shellfish from production sites receiving contaminated human waste, but commercially traded seafoods are unimportant in the epidemiology of cholera. There is also high risk of septicaemia (V. vulnificus) from ingestion of contaminated raw bivalves, especially oysters, and contact with contaminated seawater; but the risk from finfish is low (WHO, in press).

Bivalve shellfish can accumulate biotoxins such as PSP (paralytic shellfish poisoning), DSP (diarrhetic shellfish poisoning) and ASP (amnesic shellfish poisoning), and become harmful to consumers; farmed shellfish are as much a risk as are wild populations. The extent of accumulation of these toxins by finfish and crustaceans in aquaculture production facilities is still not clear. Finfish commonly produced through aquaculture will not survive exposure to PSP and therefore do not pose a risk to consumers. At present, there is very little aquaculture production of species that have the potential to be toxic (e.g. tetrodotoxin in puffer fish).

Many chemo-therapeutants are used to treat fish and the environment in which fish are grown, to control diseases and pests. The chemicals used are selected to have low toxicity to fish and they would also have low toxicity to humans. In extensive aquaculture systems, there has not been any significant use of chemotherapy, and in sophisticated, intensive production systems, the use of vaccines, coupled with changes in husbandry practices--lower stocking densities, rotation of sites and fallowing--has reduced the incidence of disease and drastically reduced the use of chemo-therapeutants (predominantly in the case of the salmon farming industry). A steady reduction in use of chemo-therapeutants, through improved husbandry, is possible and in progress in many areas (WHO, in press). While therapeutant residues resulting from aquaculture treatments may not appear to be a significant hazard to humans when considering the extremely small number of cases reported, producers must be alert to the significant public concern created by potential residues (Armstrong, 1997).

There is global concern about the consumption of low levels of antimicrobial residues in aquatic foods and the effects of these residues on human health (Reilly et al., 1997). There are now reports of plasmid-mediated antibiotic resistance among bacteria found in fish farms, and transfer of this resistance to organisms not directly in contact with the antibiotics. The danger is that illnesses in humans caused by antibiotic-resistant organisms derived from aquatic products, or the environment of aquaculture systems, might not respond to medical treatment (Howgate, 1997). This is of special concern in countries where regulations for the use of antimicrobials exist but may not be effectively enforced, and where no regulations exist at all.

There is evidence that antimicrobial-resistant strains of fish pathogens have developed over the time in which antimicrobials have been used to control fish disease (WHO, in press). In general, however, it is difficult to evaluate evidence of antimicrobial resistance because of the different methods used in the published literature. There is little agreement as to how resistance in fish pathogenic bacteria should be defined and no consensus as to how it should be measured. There is need for developing widely accepted standard methodologies (Smith et al., 1994). In addition, since studies are often of a qualitative nature, there is a tendency to report potential risks rather than to assess their importance objectively (Smith et al., 1995).

Where the use of chemo-therapeutants is necessary (i.e. where vaccination is not an option), the approach to avoid major risk to consumers is addressed in the Codex Commission document: proposed Draft Code of Hygienic Practice for the Products of Aquaculture (FAO, 1996).

In general, aquaculture in inland waters carries a greater risk of contamination from agro-chemicals, while aquaculture in estuaries is more susceptible to contamination from industrial pollutants. Two classes of pollutants are of concern with respect to human health: heavy metals and chlorinated hydrocarbons. Unfortunately, there is little information on their levels in cultured fish to allow risk assessment. With regard to heavy metals, methylmercury is of the most concern to human health. In this regard, it is likely that aquaculture products are safer than their wild counterparts, since mercury accumulates with time and aquaculture products, especially crustaceans, are harvested at a young stage. Nevertheless, bearing in mind that aquatic products are major contributors of mercury in humans, there is a clear need for more information about the mercury content of aquaculture products and the influence of aquaculture practices on it.

The chlorinated hydrocarbons of most concern for human health are the chlorinated insecticides and their degradation products, and the polychlorinated benzodioxans and furans. The use of chlorinated pesticides has been phased out in developed countries, but they may still be in use in some developing countries, or have been phased out only recently. PCBs and similar highly chlorinated industrial chemicals have not been manufactured and used to the same extent in developing countries where most freshwater aquaculture is concentrated, although they are distributed in the atmosphere on a global basis. Available information is restricted to levels of these chemicals in wild fish.

According to modern public health concepts of prevention and control of food-borne diseases, consumer hazards derived from food intake should be considered under a HACCP (hazard analysis critical control point) perspective. The HACCP system is applied from production to consumption and offers a systematic sequential approach to the control of food-borne hazards, avoiding the many weaknesses inherent in the traditional inspection approach.

The draft Code of Hygienic Practice for the Products of Aquaculture, prepared by FAO, is presently under review by the Codex Committee on Fish and Fishery Products, aiming at including HACCP principles into the document. The new text will give particular attention to biological agents such as bacteria (Salmonella spp., Vibrio spp.) and parasites (Clonorchis sinensis) of human health significance, chemical contaminants (heavy metals, agricultural pesticides, industrial chemicals) and residues of veterinary drugs (antibiotics).

Identification of ways and means to bring about the application of HACCP-based safety control systems to some types of aquaculture systems may pose a major challenge. HACCP requires that the hazards of a product or process be identified, that means of controlling the hazards exist, and that there are procedures for monitoring the effectiveness of the control measures. These conditions do not apply fully to all hazards and all current aquaculture practices (Howgate, 1997). Further, when carrying out an HACCP evaluation of a system, it is necessary to consider, in addition to the hazards, the risks; that is, the probability that the hazards would cause disease in humans (Ozonoff and Longnecker, 1991; Ahmed, 1992; Hathaway, 1993; Rose, 1995). It is not possible to calculate these risks for most of the production from aquaculture because there is little quantitative data on the intensity or extent of the hazards, and little epidemiological data on which to base estimates of the risk (Howgate, 1997).

It may not be difficult to apply the HACCP-based system to large-scale commercial aquaculture ventures. However, in small-scale, subsistence aquaculture systems, where fish are mainly farmed for domestic consumption under minimal inputs, knowledge and assistance, application of an effective HACCP-based system will pose considerable difficulties. Therefore, the design and implementation of HACCP systems should be considered following careful evaluation of the feasibility of applying such a control system to a particular aquaculture system, the risks associated with the systems components and procedures, and the identification of the correct and appropriate critical control points (WHO, in press). The HACCP approach is unique for every product and for every production unit: in each case a detailed study of the fish farming methods, inputs and production conditions is required, and the sequential flow is necessary to identify hazards and the critical control points.

The industry and government in the USA have succeeded in developing comprehensive HACCP plans for selected aquaculture products, i.e. catfish, crawfish and molluscs. A similar approach is being initiated in a few other countries, i.e. Australia, Chile, New Zealand, Norway and Thailand. FAO is carrying out studies on the use of HACCP for the control of fish-borne trematode infections in pond-raised carp in Thailand and Vietnam, in endemic areas affected by clonorchiasis and opisthorchiasis.

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