A. Reilly¹ , C. Lima DosSantos² and Michael Phillips³

¹ Food Safety Unit, WHO, Geneva
² Fisheries Industries Division, Fisheries Department, FAO
³ Network of Aquaculture Centres in Asia-Pacific (NACA), Bangkok

Introduction

Over the past decade, we have begun to see the supply of food fish from capture fisheries levelling out, and have witnessed a rapid expansion in aquaculture production. The fisheries sector is undergoing the same transition as the food animal production sector, in that man no longer hunts for meat: in future years, we will rely to a far greater extent on farmed fish as a source of protein foods of high nutritional value. Epidemiological evidence of foodborne diseases suggests that fish harvested from open oceans can be generally regarded as safe and nutritious foods, provided that these are chilled quickly and handled properly. Products from aquaculture on the other hand have sometimes been associated with certain food safety issues, as the risk of contamination of products by chemical and biological agents is greater in freshwater and coastal ecosystems than in the open seas.

Food safety issues associated with aquaculture products will differ from region to region and from habitat to habitat and will vary according to the method of production, management practices and environmental conditions. Foodborne parasitic infections, foodborne disease associated with pathogenic bacteria, residues of agro-chemicals,

veterinary drugs and heavy metal contamination have all been identified as potential hazards of aquaculture products. The origins of such food safety concerns are diverse, ranging from inappropriate aquacultural practices, environmental pollution and cultural habits of food preparation and consumption. Thus, with the increasing contribution of aquaculture to food fish supplies and to regional and international trade, proper assessment and regulation of any food safety concerns are becoming increasingly important.

Against this background, FAO and WHO, together with the Network of Aquaculture Centres in Asia - Pacific (NACA) organized a Study Group of experts to consider food safety issues associated with farmed finfish and crustaceans, particularly those associated with biological and chemical contamination. The organizers recognized the complexity of the tasks of preventing and controlling food safety hazards associated with products from aquaculture and thus invited experts from 15 countries from a broad range of disciplines and backgrounds. The meeting considered the identification and quantification of hazards and how to implement measures for control of potential food safety hazards, including current national and international programmes.

This article is based on the report of and material presented at the Joint FAO/NACA/WHO Study Group on Food Safety Issues Associated with Products from Aquaculture² held on 22^nd-26^th August 1997 In Bangkok, Thailand. The authors were co-secretaries of the meeting.

  ¹ See also related news in
FAN No. 17,
  December 1997, p. 23.

² The full report is in press and will be published later this year by WHO in the Technical Report Series (available from WHO, Distribution & Sales, CH-1211, Geneva 27, Switzerland).

Hazards and risks

Inherent in all human activities, including activities related to food production, there are hazards and risks which may adversely affect human health, and aquaculture is no exception. In this context it is particularly important to recognize that there is a fundamental difference between hazard and risk. 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 the adverse health effects in exposed populations, consequential to hazard(s) in food. Understanding the association between a reduction in hazards that may be associated with food, and the reduction in the risk to consumers of adverse health effects is of particular importance in the development of appropriate food safety measures. The hazards identified by the Study Group are summarized in Table 1.

these parasites are trematodiasis, cestodiasis, and nematodiasis.

Fishborne trematodiasis is an important disease in various parts of the world. Data from WHO ( WHO, 1995) suggests that over 40 million people, mainly in eastern and southern Asia, are affected and more than 10% of the world population are at risk of infection. Freshwater capture fisheries are known to be an important source of infection, and little information is available on the role of farmed finfish and crustaceans in the spread of diseases associated with the ingestion of these parasites. The route of infection is through the ingestion of viable encysted metacercareae of parasites, which are present in the flesh of raw, inadequately cooked or minimally processed freshwater fish. The two major genera of importance for human health are Clonorchis and Opisthorchis, and of lesser importance Paragonimus, Heterophyes and Metagonimus.

Table 1. Possible food safety hazards in aquaculture products

Biological Hazards

A large number of fish species, both marine and freshwater, may serve as a source of medically important parasites. Some of these parasites are highly pathogenic and the main cause of human infection is the consumption of raw or inadequately cooked fish. It was evident from the meeting that these infections are prevalent in only a few countries in the world and essentially among communities where eating raw or inadequately cooked fish is a cultural habit. Generally, fish are the intermediary hosts of these parasites, and man becomes the definitive host when the parasites are ingested. The principle

human diseases caused by Pathogenic bacteria can be introduced into fish ponds and watercourses by the intentional or unintentional addition of human and animal wastes. While evidence was presented at the Study Group that enteric bacteria and viruses rapidly die-off in well managed fish ponds, some evidence exists which suggests that enteric pathogens can survive and contaminate farmed products. Naturally occurring pathogens, such as Vibrio parahaemolyticus and Vibrio cholerae can contaminate aquaculture products, particularly in warm water climates, and have been implicated in fishborne illnesses.

Chemical hazards can be present in aquaculture products through exposure to certain compounds used in the aquaculture system itself and by acute and chronic pollution of waterways or sources of water used. A broad range of chemicals are used in aquaculture - chemical fertilizers are widely applied to semi-intensively managed ponds to stimulate phytoplankton blooms. Such fertilizers may be either organic or inorganic in nature and are usually water soluble. They can be applied as individual compounds, or they may be blended to provide a mixed fertilizer containing two or more compounds. Although some of these compounds may be considered as hazards in their own right, in view of the concentrations and methods of use, the Study Group concluded they pose minimal risk to food safety in aquaculture products when used appropriately. Similar conclusions were reached regarding a range of water treatment compounds used in aquaculture production.

The Study Group recognized that the use of antimicrobial agents in the aquatic environment is a cause for concern, both in terms of potential environmental risk and potential human health implications. The main concerns are associated with the unregulated sale and use of antibiotics as therapeutic agents, growth promoters and for increasing the efficiency of feed utilization in intensive and semi-intensive aquaculture systems. The hazards relate to veterinary drug residues and the development of antimicrobial resistance deriving from the use of antimicrobial agents.

However, limited data exists on the health risks associated with the use of antimicrobials in aquaculture, which precludes quantitative assessment of risk. Residues in products can be controlled by following recommended withdrawal times. The possible transfer of antimicrobial resistant pathogens to humans arising from the use of veterinary drugs in temperate water aquaculture was thought to be low, but maybe higher in tropical aquaculture, but only where antibiotics are used, because of higher temperatures and the survival of enteric human pathogens in fish ponds.

Food safety from fish farm to table

The role of the fish farmer is changing from merely raising fish to being an indispensable part of a chain for the production and delivery of safe, high quality products to the consumer. Hazards can be introduced into this food chain at the production stages, on the farm, and these can be spread during fish processing and preparation. Intervention strategies for assuring food safety are difficult to determine when microbial hazards cause human diseases but no diseases occur in fish, as in the case of some naturally occurring pathogenic Vibrio spp. or unavoidable contamination of fish ponds by Salmonella spp. in some aquaculture systems. Quantitative risk assessment is thought to be the most effective method of identifying contamination by

microbial pathogens and this data could be used in making risk management decisions. Although this is an emerging discipline, data generated by microbial risk assessment can be used in the application of food safety assurance programmes based on the Hazards Analysis and Critical Control Point (HACCP) system. While the implementation of HACCP-based safety assurance programmes are well advanced in the fish processing sector, the application of such programmes at the fish farm, to enhance food safety, is in its infancy. The fish farming sector is not unique in this respect as there are few examples of the application of HACCP principles in animal husbandry because of the lack of scientific data regarding the appropriateness of on-farm control for pathogenic micro-organisms.

There is an international movement towards the adoption of the HACCP system in the seafood sector, with such major markets as the European Union and North America introducing mandatory requirements for HACCP implementation during fish processing. Such requirements will impact on the aquaculture sector with respect to raw material standards and products moving in international trade. The introduction of HACCP-based food safety assurance programmes, at fish farm level, poses a major challenge to the aquaculture sector. With the current state of knowledge, the introduction is practical, and is being applied in some intensive aquaculture systems, but not possible in small-scale fish farming systems that account for the bulk of global aquaculture production.

The report of the Study Group includes a generic model for the application of the HACCP system to aquaculture production.

Knowledge gaps and research needs

The Study Group concluded that there were considerable needs for information on food safety hazards associated with this rapidly expanding sector of food production. Such gaps in knowledge will hinder the process of risk assessment and the application of appropriate risk management strategies with respect to food safety assurance and products from aquaculture.

Biological hazards

Parasites

The Study Group recognized the importance of trematode and, to a lesser extent, cestode and nematode parasites as public health problems, particularly in Asia. It also recognized that little information is available on the role of farmed finfish in the spread of diseases associated with the ingestion of these parasites. Indeed, culture of fish under appropriate environmental and management regimes,

unlike capture fisheries, offers a potentially important way to control this problem in some freshwater fishes.

Further research needs to be conducted on the epidemiology of trematode infections in cultured fish in relation to foodborne illness. Prior to establishing the comparative risk to human health from consumption of farmed and wild fish, it is necessary to determine the levels of trematode infection in farmed and wild fish and the influence of cultural practices of fish consumption. Research on the elimination of parasites in fish during processing should be given importance, particularly to determine the ability of the infective stages of these organisms to survive heat treatment. Freezing as a method to eliminate hazards associated with parasites in fish should be evaluated with respect to the possibility of allergic reactions and hypersensitivity. More work is required to quantify the levels of infection of farmed fish by parasites and to evaluate the contribution of aquaculture products to foodborne trematode infections.

Stocking fish ponds with wild caught fry or allowing wild fish to enter ponds is common practice in many areas. Epidemiological data should be obtained to evaluate the association of trematode infections in humans with such farming practices.

Bacteria

The Study Group concluded that unavoidable contamination of aquaculture products by foodborne pathogens, such as Salmonella and Vibrio can occur in some farming systems. Studies are required to apply molecular typing methods to distinguish between these and pathogens of human origin that may occur in products as a result of poor standards of hygiene during post-harvest handling and processing. There is also a need for methods to be developed for the detection of enteroviruses in aquaculture systems.

In view of the increasing importance of wastewater-fed aquaculture systems in developing countries, the potential for the growth and survival of human enteric pathogens, particularly newly emerging strains of Escherichia coli, needs to be investigated.

In light of international trade of foods, microbiological risk assessment methods are required in many areas of food production and processing. The Study Group noted that such

work was underway in the Codex Committee on Food Hygiene and recommended following the Codex guidelines for the conduct of microbiological risk assessment for products from aquaculture.

The evaluation of such risks is constrained by the lack of quantitative data. Specific areas in aquaculture where the Study Group identified the application of risk assessment methods are the use of moist animal-based feeds (e.g. trash fish, bivalves, and slaughterhouse waste); the ecology of Listeria in salmon aquaculture; the risks to public health from antibiotic resistant bacteria developing as a result of applying antibiotics in aquaculture; integrated animal husbandry/fish farming; and wastewater fed systems.

Chemotherapeutants

The Study Group identified the following research needs for the safe and effective use of chemicals in aquaculture:

• With respect to antimicrobial resistance, internationally agreed-upon and validated methods to determine the minimum inhibitory concentration (MIC) are needed. Support from international bodies such as FAO and WHO would assist progress in this area.

• Agreed-upon and validated methods of residue analysis that do not impose excessive cost on consumers or producers are needed for compliance monitoring.

• Due to the limited number of approved veterinary medicines for use in intensive aquaculture in some countries, research is needed to enable products approved in one regulatory regime to be used in another without the cost of duplicate approval procedures.

• Certain types of integrated fish farming systems, where antibiotic-fed livestock are used, may pose a risk of antimicrobial resistance or unexpected residues in fish. The health implications of this type of artisanal production, combined with antimicrobial use is poorly understood and more information is needed before a proper assessment can be made.

Reference: WHO 1995. Control of food born trematode infections. Report of a WHO Study Group, Manila, Philippines, 18-26 October 1993. Geneva, WHO.)

MAIN CONCLUSIONS

The main conclusions from the meeting were that :

ª aquaculture production will certainly become an increasingly important means of producing aquatic products for human consumption;

ª fish-borne trematodiasis is an important disease in some parts of the world, causing morbidity and serious health complications. Basic research is required on the survival of encysted metacercareae of these parasites in edible portions of fish during traditional processing and preparation; FAO/WHO were requested to co-ordinate research in this area.