Fish Health and Welfare

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Subtopics Healthy Animal gives a Better Food Farm Conditions - avoiding stressors is a key prevention strategy Humane Slaughter - preserving animal welfare and avoiding suffering Health Treatments - increasingly based on enhancement of the animal immune response

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Health Treatments - increasingly based on enhancement of the animal immune response

In the past, health treatments were based on chemical products and a reactive behaviour to diseases. The emphasis is now on a proactive behaviour and better management for prevention, which is likely to be more cost effective than treatment, involving both on-farm management and the management of the environment where farms are located. There is considerable scope for further improvement in developing new disease control tools and perfecting existing ones. Among others, areas for health treatments include:

1. Harnessing the host's specific and non-specific defence mechanisms in controlling aquatic animal diseases
2. Development of affordable yet efficient vaccines for economically important tropical fish
3. Use of immuno-stimulants and non-specific immune-enhancers to reduce susceptibility to disease
4. Use of probiotics and bioaugmentation for the improvement of aquatic environmental quality.

The results of this research will undoubtedly help reduce chemical and drug use in aquaculture, and will not only contribute towards reducing negative environmental impact of chemical use, but will also make aquaculture products more acceptable to consumers.

The first step in disease management in aquaculture systems must be to consider creating and maintaining a good living environment for the fish. Prevention is the best approach to avoiding diseases. A health management program includes quarantine, hygiene, health monitoring and disinfections when appropriate. Treatments should only be used after a proper diagnosis. Many disease treatments can have an adverse effect on the water quality of the fish farm. If the treatment is not done properly e.g. incorrect dose or duration, this can have negative effects on the stock. The disease can reappear. Environmental factors and poor water quality resulting from increased effluent discharge, movement of aquatic animals, inadequate farm management, rapid proliferation of farms, etc. have been implicated in major disease outbreaks occurring in epizootic conditions. However, the underlying causes of such epizootics are highly complex and difficult to pinpoint. An understanding of the relationship between host, pathogen and environment is important in this regard. Aquatic animals are intimately connected with their environment and husbandry practices. It is important to understand how the system in which the organisms are in, in order to control and make a diagnosis.

Since aquatic animal disease is the end result of a series of linked events, treatment of disease should go beyond consideration of the pathogen alone. Conventional approaches have so far had limited success in the prevention or cure of aquatic disease. Recent experience in trying to control disease outbreaks clearly demonstrates the importance of the linkage with other components of the production system, including the need for broader ecosystem management approaches to control farm-level environmental deterioration and to take preventative measures against the introduction of pathogens--the "systems management approach" (SMA) to aquatic animal health.

The emphasis should be on better management for prevention, which is likely to be more cost effective than cure, involving both on-farm management and the management of the environment where farms are located. Government inputs are essential for regulation of resource use, particularly land and water, and for helping to provide legal and institutional arrangements that minimize resource-use conflicts and control environmental impact of, and on aquaculture. Wider adoption of such approaches may lead to sustainable solutions that can be adopted by farmers, and to less reliance on the use of chemicals, which largely treat the symptom of the problem and not the cause. In addition, research, training programs, extension, and information exchange can be more effective and responsive to farmers' needs if based on SMA. The FAO's Code of Conduct for Responsible Fisheries is an ideal platform to link SMA and national/international cooperation in harmonising aquatic animal health management activities. There is considerable scope for further improvement in developing new disease control tools and perfecting existing ones. Major areas for further research include:

1. Quality control and more efficient and cost-effective use of inputs, such as water, seed and feed
2. The role of good nutrition in improving aquatic animal health
3. Harnessing the host's specific and non-specific defence mechanisms in controlling aquatic animal diseases
4. Development of affordable yet efficient vaccines for economically important tropical fish
5. Use of immunostimulants and non-specific immune-enhancers to reduce susceptibility to disease
6. Use of probiotics and bioaugmentation for the improvement of aquatic environmental quality.

The results of this research will undoubtedly help reduce chemical and drug use in aquaculture, and will not only contribute towards reducing negative environmental impact of chemical use, but will also make aquaculture products more acceptable to consumers. The abandonment of the use of antibiotics and chemicals is becoming a trend in the aquaculture industry, as several reasons recommend the choice of the strategies cited above rather than maintaining these treatments.

-The cost is very relevant. The antibiotics are not cheap and aquaculture is an industry with a high number of individuals

-The cost and labour demand of antibiotic administration is very important, and aquaculture farms have to carefully calculate these costs as they may be unaffordable or have a very low cost-benefit

-The animals may develop resistance to antibiotics, as this has been a trend in other farming industries

-There is a clearance period after the antibiotic treatment in which the product cannot go out of the farm to be commercialised. Therefore, it increases both the time to market and costs.

In the last years, a number of techniques have been in progress to better monitor and prevent the occurrence of pathologies, mostly based on the early detection of the indicators of immune system: Immunological assays, including fluorescent antibody techniques (FAT) and enzyme linked immuno-sorbent assays (ELISA), are presently used for sensitive and rapid detection of various fish pathogens. In addition, new assays using DNA methods and nucleic acid probes are evolving from medical diagnostics. Reports have shown that polymerase chain reaction (PCR) techniques combined with DNA probes, are effective in detecting the presence of nucleic acid sequences of fish and shrimp pathogens from infected tissues. The recent development of PCR systems for the detection of certain viruses is a major breakthrough in combating the viral epizootics. There are two trends:

1. Kits are becoming available for farmers to use on location to obtain information quickly about the presence of pathogens
2. Central laboratories with trained staff are being organised to receive fresh and preserved samples from distant locations for processing and identification of unusual or difficult-to-detect antigens or nucleic acid sequences.

Over the next decade, the potential for developing cost-effective and affordable, yet sensitive and effective, rapid diagnostic tools for use in developing-country situations will increase, as will joint commercial ventures between developed and developing countries for this purpose. The application of genetic technologies in aquaculture is a recent practice for all but a few aquatic species. These technologies can be applied as part of the fish health strategy, to increase disease resistance by selecting these strains with better resistance to pathologies or better adaptation to the farm environment.

Extract from FAO Fisheries Department Review of the state of world aquaculture health management. Need for a new approach to health management . Subasinghe, R ., FAO Fisheries Circular No. 886 FIRI/C886(Rev.1). http://www.fao.org/docrep/003/w7499e/w7499e23.htm

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