Influence of fish health management

Influence of fish health management:
Bases, procedures and economic implications
M.M. Blanco, A. Gibello and J.F. Fernández-Garayzábal
Departamento de Patología Animal I (Sanidad Animal), Facultad de Veterinaria
Universidad Complutense, 28040 Madrid, Spain
SUMMARY – As aquaculture assumes an expanding role in meeting consumer demands for fishery products, it is
natural that they meet safety and quality standards. In addition to residues of agro-chemicals, veterinary drugs
and heavy metal organic and inorganic contamination, infectious fish diseases represent one of the most
important problems and challenges in aquaculture production, both from an economic and sanitary point of view.
Diseases increase cost and reduce profit because of loss in dead fish, cost of treatment or decreased growth rate
of diseased and convalescent fish. The fish is usually exposed to pathogens or potential pathogens, but in fish
diseases, a simple association between the pathogen and the host fish does not occur. Environmental
circumstances that arise in intensive fish farming systems represent a considerable stress, making fish more
susceptible to a wide variety of pathogens. In aquaculture, many of the potential hazards at the production level
can be controlled by good fish farm management practices, which control infectious diseases and improve the
safety of the products. Successful fish health management starts with prevention of disease rather than treatment,
and this is accomplished through the implementation of integrated measures at the production level. This global
management will contribute to produce safer fish products.
Key words: Aquaculture, health management, fish diseases.
RESUME – "Influence de la gestion sanitaire du poisson : bases, procédures et implications économiques".
Tandis que l’aquaculture assure un rôle grandissant pour satisfaire les exigences des consommateurs concernant
les produits aquacoles, il est naturel qu’ils répondent aux normes de sécurité et de qualité. En plus des résidus
des produits agrochimiques, des médicaments vétérinaires et de la contamination organique et inorganique des
métaux lourds, les maladies infectieuses des poissons représentent l’un des plus importants problèmes et défis
de la production aquacole, tant du point de vue économique que sanitaire. Les maladies augmentent le coût et
réduisent le bénéfice à cause des pertes en poissons morts, du coût du traitement ou d’un taux de croissance
diminué pour les poissons malades ou convalescents. Les poissons sont généralement exposés à des
pathogènes ou pathogènes potentiels, mais pour ce qui est des maladies des poissons, ce n’est pas une simple
association entre le pathogène et le poisson-hôte. Les circonstances environnementales qui ont lieu en général
dans les systèmes d’élevage aquacole intensifs représentent un stress considérable, et rendent les poissons plus
vulnérables à une grande variété de pathogènes. En aquaculture, une grande partie des risques potentiels au
niveau de la production peuvent être contrôlés par de bons usages de gestion des fermes aquacoles, qui
représentent une bonne façon de contrôler les maladies infectieuses et d’améliorer la sécurité des produits. Une
bonne gestion sanitaire des poissons commence par la prévention des maladies plutôt que le traitement curatif, et
ceci se fait en mettant en place des mesures intégrées au niveau de la production. Cette gestion globale
contribuera à produire des produits aquacoles plus sûrs.
Mots-clés : Aquaculture, gestion sanitaire, maladies des poissons.
Aquaculture is one of the fastest growing food-producing sectors, providing an acceptable
supplement to and substitute for wild fish. During the past years the total production of cultured finfish
and shellfish have increased in production quantity and value. Global aquaculture production is
estimated at nearly 10 million metric tons annually, and it contributes more 12% of the total consumed
fish and shellfish (Pérez and Rodríguez, 1997). In general, although the global contribution of
aquaculture by quantity to total world aquatic production, the relative importance of aquaculture to
national aquatic production varies greatly. Regional, cultural and historic attributes have influenced
both the production base and rate of expansion of aquaculture. The historic tradition of growing fish in
Asia has played a significant role in maintaining its dominant position. In Europe, the aquaculture
production has significantly increased both in production quantity and value during the last years. In
the European Union, Norway and France are the countries with highest aquaculture production (20%
each of the total UE production), followed by Italy (16%), Spain (10%), UK (6,5%) and The
Netherlands (6%) (Rana, http://www.fao.org/fi/publ/circular/c886.1/tren886.asp). The main types of
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fish production in Europe are salmonid sea cage farming (salmon), sea farming of non-salmonid fish
(sea bass, sea bream and turbot), rainbow trout raceway farming, continental pond farming (carp,
crucian carp, tench) and intensive recirculating units (eel, tilapia) (Bernardet, 1998).
No animal production programme has ever been successfully performed without considering
animal health. Diseases are considered the most limiting factor to aquaculture production, both from
an economic and sanitary point of view. There are two types of disease that affect fish, non-infectious
(environmental, nutritional or genetic), and infectious diseases. These latter are contagious and
represents the most important diseases in aquaculture because they increase the cost production due
to the losses in dead fish, costs of treatments or decreased growth rate of diseased and convalescent
fish. As previously observed in other animal production systems undergoing similar changes, the
intensification of fish farming combined with the introduction of news species through the routes of
commercial exchanges, has inevitably led to the increase of some infectious diseases and to the
emergence of others, all favoured by the high stocking densities and stress of intensive farming. It is
difficult to evaluate the real economic losses, due to the different factors related; however, it has been
estimated that 10% of all cultured aquatic animals are lost as a result of infectious diseases (Leong
and Fryer, 1993). In addition, food-borne infections associated with pathogenic microorganisms have
been identified as possible hazards in aquaculture products. These hazards are generally associated
with the general condition of the environmental habitat, the species being farmed, and cultural habits
of food preparation and consumption.
Infectious diseases are caused by pathogenic organisms (parasites, bacteria, virus and fungi)
present in the environment or carried by other fish. In fact, fish are usually exposed to pathogens or
potential pathogens, but in fish diseases a simple association between the microorganism and the
host fish does not occur. Infectious disease results from a series of complex interacting variables of
the pathogen, host and environment. Many characteristics of pathogens are directly relevant in the
disease development (Hedrick, 1998). These include whether the microorganism is always associated
with infection of the host ("obligate") or whether it can survive in the absence of the host ("facultative").
The virulence of the pathogen depends on the strain, biotype, serotype or genotype of the agent
(Engelkin et al., 1991). The occurrence of the disease upon interaction of the pathogen with the fish
depends on several host factors such as age, size, development stage, nutritional and reproductive
statuses and immunological defences of the host. Moreover, there are many other predisposing
factors which contribute in the development of the infectious disease. Environmental circumstances
(poor water quality, changes in temperature, poor nutrition, crowding, transporting, etc) usually
produced in intensive fish farming systems, represent a considerable stress making fish more
susceptible to a wide variety of pathogens (Reno, 1998).
The most important factor involved in fish health management is water quality. Fish perform all their
bodily functions in water. Because fish are totally dependent upon water to breathe, feed and grow,
excrete wastes, maintain a salt balance, and reproduce, understanding the physical and chemical
qualities of water is critical to successful aquaculture. Non-infectious diseases are commonly found as
a result poor water quality. The quantity of available dissolved oxygen, the pH, and the amount of
waste products are the most important factors to be considered (Richards, 1983). Available dissolved
oxygen is probably the most critical of these, being affected by the temperature, the origin of water
and the biological demand (i.e. high concentrations of bacteria and decaying matter). The pH of the
water should be stable and just below 7. The level of waste products should be low and particular
attention paid to the presence of excessive carbon dioxide which will be toxic to the majority of fish,
and a build up of ammonia may cause the pH to go above 7.5 (Cawley, 1983). On the other hand,
water is usually a vehicle of microorganisms which are potential pathogens for fish and/or humans.
The level of contamination of aquaculture products by pathogenic agents will depend on the
environment and the microbiological quality of the water where the fish is cultured. There are two
broad groups of microorganisms of public health significance that will contaminate products of
aquaculture: those naturally present in the environment, and those introduced through environmental
contamination by domestic animal excreta and/or human wastes. Non-indigenous microorganisms can
be introduced into aquaculture ponds via unavoidable contamination by birds and terrestrial animals
associated with farm waters, and significant numbers of these remain on the skin and in the gu