safety and Products from aquaculture1
A. Reilly1 , C. Lima DosSantos2 and Michael Phillips3
1 Food Safety Unit, WHO,
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.
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
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 22nd-26th August 1997 In Bangkok, Thailand. The authors were co-secretaries of the meeting.
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
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.
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.
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
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.
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.
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.
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.
underway in the Codex Committee on Food Hygiene and recommended following the Codex
guidelines for the conduct of microbiological risk assessment for products from
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.)
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 there is a need for an integrated approach to properly identify and control hazards associated with products from aquaculture which requires close collaboration between the health, agriculture and aquaculture, food safety, and education sectors;
ª food safety assurance measures should be included in fish farm management programmes and should form an integral part of the fish "farm-to-table" food safety continuum;
ª the food safety assurance measures should be based on the Hazards Analysis and Critical Control Point (HACCP) system, although all participants recognized the difficulty in applying such measures to rural subsistence aquaculture;
ª the risks to human health from chemicals used as fertilizers and water treatment compounds in aquaculture production are low;
ª risks from chemotherapeutants used in aquaculture are associated with residues in edible portions of fish flesh and these can be significant, especially in countries where the sale and use of these compounds are uncontrolled;
ª there is the added risk of antimicrobial resistance developing in the bacterial flora of fish farms and of such antibiotic resistant bacteria entering the food chain;
ª pesticides required in aquaculture can pose food safety hazards; more information is needed on the types of compounds used, and studies should be conducted to determine if pond treatments with pesticides result in residue levels that are potentially harmful to human health;
ª there is an urgent need to raise the awareness of the fish farming community, especially small-scale rural subsistence farmers, on management strategies for producing safe aquaculture products;
ª education in the basic principles of food safety assurance should be integrated into existing regional and national training courses for aquaculture development and FAO/WHO are urged to provide leadership in developing education materials;
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.