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Importance Of Health Management In Aquaculture

Vikash Kumar1, Suvra Roy1, Debtanu Barman2

1, 2Central Institute of Fisheries Education, Mumbai, India, 400061. 3College of Fisheries, Central Agricultural University, Lembucherra, Tripura-799210, India


Introduction

Aquaculture is the farming of aquatic organisms including fish, molluscs, crustaceans and aquatic plants. Farming implies some sort of intervention in the rearing process to enhance production, such as regular stocking, feeding, protection from predators, etc. Aquaculture has a long history. In the People's Republic of China (PR China), common carp were raised for food in freshwater ponds as early as 1100 b.c. Other examples of early aquaculture practices include the Japanese culturing oysters for pearls; ancient Egyptians stocking ponds with fish; the Greeks and Romans raising eels; the Europeans cultivating oysters. The aquaculture sector is highly diverse in terms of:

  1. Species- an estimated 230 species of fin fish, molluscs, crustaceans, aquatic plants, turtles, frogs, etc. are cultured.

  2. Culture systems- e.g., water-based systems, such as cages and pens, bottom/pole/rack/raft/long-line systems for molluscs, inshore and off-shore; land- based systems such as rain-fed ponds; irrigated or flow-through systems, tanks and raceways; land/ water-based systems, such as sea ranching; recycling systems such as high control enclosed systems, more open pond-based recirculation; monoculture and polyculture systems; integrated farming systems, such as livestock- fish, integrated agriculture-aquaculture, livestock-aquaculture.

  3. Culture environment- e.g., freshwater, brackish water, marine; inland, coastal and oceanic; temperate to tropical.

  4. Type of operation and scale- e.g., small-scale backyard ponds and hatcheries to commercial operations; hatchery holding of broodstock and production of seed, nursing systems, grow-out.

  5. Intensity of practice- e.g., extensive, semi-intensive, intensive.

  6. Type of management- from family to corporate ownership.



Health as a constraint to aquaculture

The current trend in aquaculture development is towards increased intensification and commercialization of aquatic production. Like other farming sectors, the likelihood of major disease problems occurring increases as aquaculture activities intensify and expand. Thus, the aquaculture industry has been overwhelmed with its share of diseases and problems caused by viruses, bacteria, fungi, parasites and other undiagnosed and emerging pathogens. Disease is now a primary constraint to the culture of many aquatic species, impeding both economic and social development in many countries. This situation can be attributed to a variety of multi-faceted and highly interconnected factors such as the increased globalization of trade in live aquatic animals and their products; the intensification of aquaculture through the translocation of brood stock, post larvae, fry and fingerlings; the development and expansion of the ornamental fish trade; the enhancement of marine and coastal areas through stocking aquatic animals raised in hatcheries; the misunderstanding and misuse of specific pathogen free (SPF) stocks (e.g. shrimps); unanticipated negative interactions between cultured and wild fish populations; poor or lack of effective biosecurity measures; slow awareness on emerging diseases; climate change; all other human mediated movements of aquaculture commodities.

However, once a pathogen or disease agent is introduced and becomes established into the natural environment, there is little or no possibility for either treatment or eradication. While consequences of "trickle" infections from wild to cultured populations have predictable consequences due to accessible hosts under cultured conditions, the consequences of culture-borne transmission to wild stocks are harder to predict. Examples of infection of cultured stocks via wild stock reservoirs for shrimp diseases and for marine finfish disease. Koi herpes virus (KHV) has recently been introduced to Indonesia and Japan. In Japan, it has caused mass mortalities not only among farmed carp but also wild carp in many rivers and lakes.

Additional examples from Japan include the following:

  • Neoheterobothrium hirame, a monogenean parasite, the original host probably being southern flounder from the United States, is believed to have been the cause of a decline in the catch of olive flounder in some parts of Japan;

  • White spot syndrome virus (WSSV) remains an important pathogen of farmed shrimp (Penaeus monodon) and has now been recovered from wild penaeid shrimps.


Transboundary aquatic animal diseases/ pathogens

Aquaculture is faced with what is known as transboundary aquatic animal pathogens/diseases (TAAPs/TAADs), which are similar to the transboundary animal diseases or TADs in the livestock sector. TAADs are diseases that are highly contagious or transmissible, having the potential for very rapid spread irrespective of national borders and causing serious socio-economic and possibly health consequences. The Office International des Epizooties (OIE) currently lists 35 pathogens/ diseases of finfish, molluscs and crustaceans that fit three major criteria in terms of consequence, spread and diagnosis. Criteria for urgent notification for the listed aquatic animal diseases are:

  1. first occurrence or re-occurrence of a disease in a country or zone of a country if the country or zone was previously considered to be free of that particular disease;

  2. or occurrence in a new host species;

  3. or new pathogen strain or new disease manifestation;

  4. or potential for international spread of the disease;

  5. or zoonotic potential.

For non-listed diseases, the criteria for urgent notification is if there are findings in an emergency disease/pathogenic agent that are of epidemiological significance to other countries.


Impact of transboundary diseases in aquaculture

Infectious diseases are constraining the development and sustainability of the aquaculture sector through direct production losses and increased operating costs and indirectly, through restrictions on trade and impacts on biodiversity. Inadequate or poorly implemented biosecurity measures have led to significant losses due to aquatic animal diseases in many countries around the world.

The impacts of aquatic animal diseases on wild populations and biodiversity that can be measured in terms of:

  • impact on aquatic community structure through changes in predator and prey populations;

  • changes in host abundance (e.g. through altered genetic demands, altered host behaviour, increased mortality, decreased fecundity, increased susceptibility to predation);

  • reduction of intra-specific genetic variation;

  • local extirpation of susceptible components of aquatic communities;

  • the possible extinctions of species.


The impacts of disease have been estimated in socio-economic terms (e.g. losses in production, income, employment, market access or market share, investment and consumer confidence; food shortages; industry failure or closure of business or industry). However, due to the frequency of occurrence and the magnitude of spread and effects, many countries are now providing some estimates of disease impacts. Losses are expressed as monetary estimates (in many cases a scale of millions of US$), percentage decrease in production, export losses, unemployment, closure of aquaculture operations and lost consumer confidence. At the regional level, ADB/NACA reported that the minimum conservatively estimated lost farm production fish diseases (such as epizootic ulcerative syndrome (EUS) of fresh and brackish water fishes, penaeid shrimp diseases and a variety of other diseases causing losses in freshwater finfish pond culture and marine cage culture).


Economic investments and opportunities in aquatic animal health

Economic impacts have also been expressed in terms of costs of investment in disease research and control and health management programmes. so far no systematic economic assessment has been carried out. In the foreseeable future, there will be increasing demand for such assessments in order to gain attention and continuous support from both the public and private sectors.


Strategies for combating diseases in Asian aquaculture

There are general strategies currently being implemented in the Asia- Pacific region (but having applicability to other regions of the world), and apply to all infectious diseases.

  1. International codes

In order to minimize the risks of pathogens/ diseases associated with aquatic animal movements, there are a number of existing global instruments, agreements, codes of practice and guidelines (either voluntary or obligatory) that, if implemented, provide certain levels of protection.

These include:

  • OIE's Aquatic Animal Health Code;

  • the Code of Practice on the Introductions and Transfers of Marine Organisms of the International Council for the Exploration of the Seas (ICES);

  • the Codes of Practice and Manual of Procedures for Consideration of Introductions and Transfers of Marine and Freshwater Organisms of the European Inland Fisheries Advisory Commission (EIFAC).



  1. Regional guidelines

Because many countries in the Asian region share common social, economic, industrial, environmental, biological and geographical characteristics, a regionally adopted health management programme is considered a practical approach. Some of the provisions in the current international protocols are not always practically applicable to the diseases of concern to the Asian region. Therefore, it was deemed important to focus on the species and diseases affecting those species. The Asia Regional Technical Guidelines on Health Management for the Responsible Movement of Live Aquatic Animals and the Beijing Consensus and Implementation Strategy (or the "Technical Guidelines") was based on a set of guiding principles developed through a regional project of FAO and implemented by the Network of Aquaculture Centers in Asia-Pacific (NACA) using a consultative process that involved representatives from 21 participating governments and technical assistance from regional and international experts on aquatic animal health. The Technical Guidelines describe a number of health management considerations aimed at minimizing the risk of disease spread via aquatic animal movements and were developed to:

  • assist countries in the Asia-Pacific to move live aquatic animals in a way that minimizes the disease risks associated with pathogen transfer and disease spread, both within and across boundaries;

  • enhance protection of the aquatic environment and biodiversity, as well as the interests of aquaculture and capture fisheries;

  • provide a mechanism to facilitate trade in live aquatic species and avoid unjustifiable trade barriers based on aquatic animal health issues;

  • implement relevant provisions of FAO's CCRF and other international treaties and agreements (e.g. WTO's SPS agreement) applicable to the Asian region.


  1. National strategies on aquatic animal health management

National strategies contain the action plans of government at the short, medium and long-term, following the concept of "phased implementation based on national needs" for the implementation of the Asia Regional Technical Guidelines. The National Strategy framework includes elements such as national coordination, legislation and policy, list of pathogens, institutional resources, diagnostics, health certification and quarantine, surveillance and reporting, disease zoning, contingency planning, import risk analysis, capacity building, awareness building and communication, farmer/private sector involvement, financial resources, monitoring and evaluation and regional cooperation. The various processes and examples of national strategies; one specific example is Australia's AQUAPLAN. Asian governments have agreed to implement the Technical Guidelines at the national level through the National Strategy framework.


  1. Diagnostics, therapy and information technology

Because of the scale of resource expertise and infrastructure required (e.g. training, facilities, resources) for disease diagnostics) recommended the use of three levels of diagnostics:

(a) Level I: field observation of the animal and the environment, clinical examination;

(b) Level II: laboratory observations using parasitology, bacteriology, mycology and histopathology;

(c) Level III: laboratory observations using virology, electron microscopy, molecular biology and immunology.

The three levels have broad-scale application to disease detection and diagnostics. Therefore, countries are encouraged to move from one level to the next as capacities are improved and as resources become available. The application of molecular-based technologies (Level III) in aquaculture health has advanced rapidly (e.g. the use of polymerase chain reaction (PCR) in shrimp and molluscan disease diagnostics). Vaccination is another established, proven and cost-effective method for controlling certain infectious diseases in cultured animals. Vaccines reduce the severity of disease losses, reduce the need for antibiotic use, leave no residues in the product and do not induce pathogen resistance. There are currently many commercially available vaccines for finfish diseases, and a few more are under development. In Japan, for example, the use of injection vaccines is now widespread among maricultured animals, proved effective against bacterial (e.g. Lactococcus garvieae infection of yellowtail) and viral infections (e.g. iridoviral infection of red sea bream) and has changed the patterns of disease occurrences. In conjunction with good health management and good husbandry practices, there is great potential for the use of vaccine technology for specific use in Asian aquaculture.


  1. Biosecurity

There will be increasing demand for improved aquatic animal biosecurity. This will be driven by multiple objectives such as resource protection (aquaculture, wild fisheries and the general environment), food security, trade, consumer preference for high quality and safe products, production profitability, investment and development issues, and new threats of emerging health problems (e.g. new diseases/ pathogens, new hosts for well-studied pathogens). Biosecurity programmes have a strong scientific basis and use risk assessment to evaluate the most significant disease hazards, their possible routes of entry, the likelihood of them becoming established, the possibilities of spread and risk management approaches in order to ensure appropriate protection. Risk analysis form aquatic animal trade provides a science-based, justifiable means to estimate the risks posed to aquaculture and aquatic biodiversity due to pathogen introduction or, in a more specific form, the risk to a particular farm unit. Such analysis makes use of scientific and technical information as a basis for policy development and decisions, and can also be used to identify knowledge gaps and thereby assist in prioritizing future research direction and priorities. The process employs sound epidemiological principles, approach and data. Epidemiology, the study of the frequency, determinants and distribution of disease, has as its ultimate objective the resolving of animal health problems. Epidemiological studies generate the data required for risk analyses; biosecurity measures require good information for accurate assessment, which leads to appropriate risk management decisions. Thus, biosecurity, risk analysis and epidemiology are highly interrelated and are all aimed at making good use of scientific research for disease prevention, control and management.



  1. Surveillance and reporting

The disease situation in aquaculture is changing rapidly in an unpredictable way due to the current period of rapid change in the international trading environment—affected by globalization, increasing aquaculture production and microbial adaptation. Thus, in this age of uncertainty due to food insecurity and bioterrorism, the use and application of "surveillance" and "reporting" has become very timely. The Asia-Pacific region is unique in that a quarterly aquatic animal disease reporting system has been established since mid-1998 by NACA and FAO in cooperation with OIE (NACA/FAO, 1999). This is an important step towards building the essential information for instituting control and eradication measures, as well as to support early warning, risk assessment, contingency plans and emergency preparedness programmes for aquatic animal diseases and epizootics. The application of disease surveillance and reporting to aquatic animal health and aquaculture is complicated by factors such as the wide ranges of socio-economic and technological development in many countries, the diversity of species cultured, the range and complexity of environments, the nature of containment, the intensity of practice, and the variety of culture systems and types of management. Although there are still problems with respect to accuracy, consistency and timely submission of reports, the system is evolving and reporting governments are starting to realize the benefits of such a system. Activities and further work are continuing towards providing assistance to regional disease surveillance, reporting and capacity building to improve the quality of the reports, and enhance effective surveillance and accurate analysis of disease reports.


  1. Emergency response to disease epizootics

The Asia-Pacific region has been plagued with many disease emergencies during the last three decades. The most significant disease emergencies include that of EUS, shrimp viral diseases (WSD, YHD, IHHN, etc.), Akoya pearl oyster mortalities, and most recently, KHV and abalone mortalities. In a way, the region has learned to deal with the emergency situation using available limited resources, expertise and facilities. Some of the important lessons and valuable insights learned from dealing with those epizootics include the need for:

  • regional and international cooperation;

  • increased awareness on emerging diseases in other parts of the globe and the possibility of their spread to the Asian region;

  • improved diagnostic capabilities at both the national and regional levels;

  • pro-active reporting of serious disease outbreaks as a mechanism for early warning;

  • contingency plans at both the national and regional levels;

  • improved compliance and implementation of policies reached at the regional and international levels;

  • emergency preparedness as a core function of government services;

  • advanced financial planning such that adequate funds can be immediately provided to address serious emergency disease situations at both the national and regional levels.


Conclusions

Addressing health questions with both pro-active and reactive programmes has become a primary requirement for sustaining aquaculture production and product trade. The current strategy in the Asia-Pacific region emphasizes responsible health management to minimize the risks of disease incursions brought about by the movement of live aquatic animals and their products. The regional Technical Guidelines provide valuable guidance for national and regional efforts in reducing these risks and a strong platform for mutual cooperation at the national, regional and international levels. There is strong support at various levels to implement the Technical Guidelines and National Strategies. The aquaculture sector will continue to intensify; trade in live aquatic animals will also persist because it is a necessity for aquaculture development at both the subsistence and commercial levels. The risk of major disease incursions and newly emerging diseases will keep on threatening the sector, and unless appropriate health management measures are maintained and effectively implemented, the government and private sectors will be faced with more costs in terms of production losses and the efforts needed to contain and eradicate diseases, funds that would have been better spent in preventing their entry into the system. Focusing efforts on prevention, on better management practices and on maintaining healthy fish maybe more important than focusing on why fish get sick. Health management is a shared responsibility, and each stakeholder's contribution is essential to the health management process.


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