D5663.PDF

Conf. OIE 1999, 227-240
PREVENTION AND MANAGEMENT OF DISEASES IN FARMED, SEA-CAUGHT AND
RECREATIONALLY CAUGHT FISH IN ASIA, THE FAR EAST AND OCEANIA
K. Nakajima
Director of Pathogen Division, Fish Pathology Department, National Research Institute of
Aquaculture Fisheries Agency, 422-1 Nakatsuhamaura, Nansei-cho, Watarai-gun, Mie 516-01, Japan
Original: English
Summary: The position of aquaculture in global fishery production is described and information on the
geographical features of aquaculture production and production by category in this region is provided.
Brief information is given on disease problems in the region. Concerning the prevention and management
of diseases, general remarks are made and emphasis is placed on the implementation of appropriate
aquaculture management. Several important points with respect to the implementation of appropriate
management are described. These include the training of aquaculture farmers, the role of guidance
institutions for aquaculture farmers and the role of research institutions. In addition, emphasis is placed
on collecting accurate epidemiological information from each country and distributing such information
within the region. Each country should possess sufficient diagnostic ability, human resources and
infrastructure to sustain diagnostic operations. Moreover, the appropriate use of drugs and vaccines and
the importance of making efforts to develop vaccines is described. Legal frameworks in this region are
discussed. White spot syndrome (WSS) in shrimps is given as an example to illustrate practical disease
control measures. The need for collecting accurate information on diseases is also mentioned. Finally,
the information on sea-caught fish and recreationally caught fish contained in the questionnaire results is
discussed.
1. INTRODUCTION
The OIE Regional Commission for Asia, the Far East and Oceania has considered it opportune to discuss the topic of
prevention and management of diseases in farmed, sea-caught and recreationally caught fish in this region.
Information on this issue has been received from Australia, India, Japan, the Republic of Korea, Malaysia, Mongolia,
New Caledonia, New Zealand, Singapore, Sri Lanka, Thailand and Taipei China. Mongolia has reported that no species
of fish are farmed in that country. All submitted information has been incorporated in this report.
In 1996, the average global consumption of fish protein represented 16% of all animal protein. Aquaculture accounted
for 22% of global fishery production and 26% of fish used as food (37). In Asia, the Far East and Oceania, there has
been a rapid increase in aquaculture production in recent years, especially in Asia.
Although an accurate figure on the losses in aquaculture production in this region due to disease is not available, this
has been considerable, especially in proportion to the increase in aquaculture production.
Due to limitations on both space and submitted information, it is not possible in this study to cover in detail all aspects
of prevention and management of diseases of farmed, sea-caught and recreationally caught fish. For this reason,
aquaculture production and the diseases reported in aquaculture in this region will only be referred to briefly.
2. FARMED FISH
2.1.
Fish farming
Production of fish and shellfish in the global aquaculture market in 1997 amounted to approximately 28,808×103
metric tons. Production in this region in 1997 totalled 25,852×103 metric tons, thus representing about 90% of
the global aquaculture production of fish and shellfish (6). In particular, production in Asia is extremely high
due to the production of freshwater fish in China (Table 1).
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Table 1: Aquaculture production in Asia, the Far East and Oceania (1997)
Country
Total
Australia
27
Freshwater fish
Diadromous fish Marine fish Crustaceans
11
2
2
Molluscs
12
Bangladesh
513
387
Cambodia
12
12
19 271
11 943
167
323
327
6 511
255
66
92
17
14
66
8
4
1 776
1 721
754
408
175
Iran
31
27
3
Iraq
3
3
Japan
798
15
61
246
2
474
Korea (Rep. of)
368
19
6
39
2
302
14
14
Malaysia
103
20
10
3
10
60
Myanmar
87
87
Nepal
12
12
New Zealand
73
China (People's Rep. of)
Taipei China
Hong Kong China
India
Indonesia
Laos
New Caledonia
Pakistan
Philippines
Russian Federation
4
55
11
160
1
4
69
2
2
22
22
330
97
161
1
54
48
4
2
Singapore
4
Sri Lanka
7
2
Thailand
575
257
Vietnam
480
369
25 579
15 533
Total
126
45
1
26
3
5
4
699
2
650
223
89
96
15
1 070
7 627
Source: Aquaculture Production Statistics 1988-1997 (FAO; ISSN 0429-9329) Unit: 1000t
As for production by category, freshwater fish accounts for 60.7%, mollusks 29.8%, crustaceans 4.2%,
diadromous fish 2.7% and marine fish 2.5% of total production, respectively (Table 1). Although the aquaculture
production volume of shrimp is less than that of freshwater fish, the shrimp farming industry has an
economically important role in the region due to the high market value of shrimp (2).
However, across this region, the features of aquaculture production in each country may differ due to differences
in climate and geographical situation.
Aquaculture production in the region is primarily characterised by the high proportion it represents in global
aquaculture production, especially the large production of freshwater fish. In addition, pond culture, using
naturally occurring ponds or closed rice fields, is thought to be another characteristic.
2.2.
Disease problems
Table 2 shows notifiable/significant diseases, which are described as diseases reported or known at present (34).
Table 3 summarizes the disease information in the questionnaire results. From these tables, one can see that there
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are many varieties of pathogens and diseases. In considering the actual situations both of aquaculture and
disease in the region, it seems appropriate to focus attention on white spot syndrome (WSS) in shrimps (7, 8, 21,
22) and epizootic ulcerative syndrome (EUS), the latter of which infects many fish species (23, 36, 38).
Table 2: Diseases reported in the Asia and Pacific Region
Disease
Country
Host
Viral diseases
Pilchard Herpes virus
Australia
Viral encephalopathy and retinopathy
Australia
Taipei China
finfish
finfish
White spot syndrome
Bangladesh
India
Japan
Korea (Rep. of)
Malaysia
Philippines
Sri Lanka
Taipei China
Thailand
Penaeus monodon
shrimp
crustaceans
crustaceans
Penaeus monodon
Penaeus monodon
crustaceans
crustaceans
crustaceans
Spawner mortality syndrome
(Midcrop mortality syndrome)
Philippines
Penaeus monodon
Infectious haematopoietic necrosis
Japan
finfish
Oncorhynchus masou virus disease
Japan
finfish
Infectious pancreatic necrosis
Japan
finfish
Yellowhead disease
Philippines
Sri Lanka
Thailand
Penaeus monodon
crustaceans
crustaceans
Japan
Vietnam
finfish
Carps
New Zealand
oysters
Australia
Bangladesh
India
Laos
Nepal
finfish
Snake head, catfish, eel, carps
genus Channa and Puntius
Morulius chrysophekadion
Silver carp, Puntius and Ophiocephalus spp,
Cirrhinus mrigala, Labeo rohita, bighead carp
Snake head, spotted sickle, mullet, catfish
finfish
Bacterial disease
Bacterial kidney disease
Parasitic infections
Bonamiosis (Bonamia sp., B. ostreae)
Fungal disease
Epizootic ulcerative syndrome (EUS)
Philippines
Pakistan
* OIE Quarterly aquatic animal disease report (October 1998-March 1999, Asian and Pacific Region)
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Table 3: Economically significant disease problems in farmed fish recorded during the last ten years
Country
Species
Diseases/disease agents
Australia
Edible Oysters
Prawns
Various finfish
QX disease, winter mortality
Vibrio sp.
Epizootic ulcerative syndrome
India
Freshwater fish
Epizootic ulcerative syndrome
Japan
Red Sea bream
Kuruma prawn
Pearl oyster
Striped beak perch
Flounder
Flounder
Freshwater fish
Red Sea bream ridoviral disease
Penaeid acute viremia (White spot syndrome)
High mortality (causes are unknown)
Iridoviral disease
Lymphocystis disease
Edwardsiellosis
White spot disease
(Protozoa: Ichchyopthrius multifilis)
Aeromonas hydrophila
White spot disease (Protozoa: Cryptecaryon irritans)
Vibriosis (V. Parahaemolyticus, V. alginolyticus and Vibrio sp.)
Yersiniosis
Vibriosis (V. Ordalii)
Flatworm/protozoan ectoparasite
Vibriosis
Viral nervous necrosis
Iridoviruses
Tetrahymena
Columnaris disease
Pseudomonas spp.
White spot syndrome
Korea (Rep. of)
Malaysia
Marine fish
New Zealand
Singapore
chinook salmon
salmon
Groupers and seabass
Groupers and seabass
Groupers (occasional)
Sri Lanka
Taipei China
Thailand
Hybrid catfish
Snakehead fish
Giant gourami
Catfish
Giant freshwater prawn
Tiger frog
Soft-shelled turtle
Giant tiger prawn
Grouper and seabass
Protozoan, monogene parasite
Aeromonas spp.
Columnaris disease
Epizootic ulcerative syndrome
Mycobacteriosis
Aeromonas spp.
Columnaris disease
Protozoan parasite
Crustacean parasite
Pseudomonas spp.
Aeromonas spp.
Mycobacteriosis
Protozoan parasite
Aeromonas spp.
Black-gill disease
Body and walking legs erosion
Aeromonas spp.
Pseudomonas spp.
Tiger frog iridovirus
Aeromonas spp.
Intestinal Protozoan
White spot syndrome
Yellow head disease
Vibriosis
Columnaris disease
Vibriosis
Viral diseases
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2.3.
Prevention and management of disease
The fundamental goal of disease control is to implement appropriate on-site aqaculture management. Aquatic
animals have frequently come to be traded in recent years. Therefore, increase in not only domestic movement,
but also international movement, heightens the risk of introducing exotic or new disease agents from infected
zones into disease-free zones (13, 14, 25, 44, 45). Confronted by these situations, some countries need to
strengthen surveillance.
The fish described in this report are classified as farmed fish, sea-caught fish and recreationally caught fish, but
a large number of fish species belong to each category. Various types of prevention and management of diseases
exist, depending on the species of the target fish, its farming method, etc. Therefore, this paper will explain the
basic principles that are common to all categories.
2.3.1. Management of farming
Infection depends on a complex correlation between pathogen virulence and various immune responses
in fish. It is also affected by poor environmental conditions, such as low dissolved oxygen (9) or
sediment composition including a high level of hydrogen sulfide. Measures to prevent infectious diseases
are conceptually divided into two groups (11):
-
enhancing the immune capacity of fish; and
blocking contact between pathogens and hosts (taking measures against sources/routes of infection).
However, use of these measures cannot be effective without correct understanding on the part of farmers
of appropriate aquaculture management, including knowledge of the prevention of infectious diseases.
These measures should also be carried out as part of daily production phases. Therefore, encouraging
ideas promoting the prevention of infectious disease is also considered as an important disease control
measure (25).
In aquaculture, a large number of fish are confined in a limited compartment, such as a pond or a net
cage. Thus measures should take into account entire ponds rather than individual fish basis.
2.3.1.1. Enhancement of immune capacity
The most basic means of fish health management is the enhancing of immune capacity.
Confining organisms that have been adapted to living in natural waters to a limited compartment
creates considerable stress and reduces immune capacity (43). To alleviate these conditions, the
following measures should be implemented:
- improvement of aquaculture facilities, such as the structure of the pond or the location of the
net cage
- implementation of sophisticated handling procedures
- rectification of the farming density
- maintenance of water/sediment quality
- improvement of feed, including nutrition
- separate farming by age of fish
Naturally, the improvement of hereditary characteristics, aimed at strengthening immunity, is
also effective as a measure against disease (5, 18). It is expected that research on this subject,
which is currently being conducted, will prove useful in the future.
2.3.1.2. Disease control measures are shown in Table 4.
2.3.2. Training of aquaculture farmers
For implementation of appropriate on-site aquaculture management, aquaculture managers need to
acquire a fundamental understanding of disease control, including, for example, knowledge of farming
animals, of feed and nutrition, and of diseases in order to make clinical observations. Knowledge of drugs
and aquaculture environment, including water quality, is also essential.
In addition, aquaculture managers should keep records of the necessary items in their daily management
operations, such as the results of close observation of farming animals, the measurement results of basic
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Conf. OIE 1999
environmental indexes and the progress of drug administrations, and put them into use in farming
management. Training on these subjects should thus be implemented for aquaculture farmers.
Table 4: Measures to be taken against sources/routes of infection (11, 33)
Main sources/routes of infection
Measures
Organisms with pathogens (including
carriers)
Detection and elimination of carriers.
Appropriate disposal of diseased/dead fish.
Environment, such as facilities
contaminated with the pathogen
Cleaning and disinfection
Natural (non-artificial) infection routes:
water, wild animals, etc.
Disinfection of water supply and drainage.
Prevention of intrusion of wild aquatic animals or vectors.
Artificial infection routes: introduction of
seedlings/ farmed fish, provision of
contaminated feeds, use of contaminated
instruments and equipment, etc.
Securing of healthy seedlings (securing of specific pathogen-free brood
stocks, disinfection of eggs/larvae/juveniles, etc.).
Securing of hygienic facilities and equipment (disinfection of transportation
instruments, culturing equipment, etc.).
Securing of hygienic feed.
Implementation of hygienic operations, including those related to humans.
Prohibition of transport of infected seedlings, etc. from an infected zone.
Implementation of inspection, detection of pathogen and attachment of
health certificate.
Import quarantine at seaports and airports.
Continuous stringent observations and quick/precise diagnoses constitute other important disease control measures.
2.3.3. Guidance institutions for aquaculture farmers
Guidance institutions for aquaculture or fish diseases include public, private, specialized fishery and
veterinary institutions, and these may vary according to each country. However, in any case, it is
necessary for each guidance institution to have an appropriate number of experts possessing sufficient
skills and expert knowledge in aquaculture guidance and who are familiar with specialized techniques.
These institutions must also provide basic facilities for diagnosis. Specifically, disease diagnoses would
require technical experts on parasites, bacteria, fungi, histopathology, etc. (provision of additional
technical experts on viral diagnosis would also be desirable). It is also necessary to provide such
technical experts appropriate education.
These guidance institutions should contact and cooperate with those scientists who are familiar with more
sophisticated techniques and possess superior knowledge, in order to receive technical advice.
Furthermore, guidance institutions should record the progress of implemented diagnoses and store the
specimens prepared for diagnosis, in order to utilize them in the event of similar disease outbreaks.
2.3.4. Research institutions
Most of the fish diseases that cause serious impact are viral in origin. Diagnosis of these diseases requires
a high level of technical expertise. Therefore, research institutions need advanced equipment for micropathology (e.g. electron microscope, cell culture equipment) or an immunological diagnostic method, as
well as technical experts with a high level of expertise in that particular field.
Meanwhile, one of the roles of such research institutions is to cooperate with guidance institutions in the
training of aquaculture farmers or technicians in guidance institutions, and establish protocols for testing
methods or the maintenance of records at guidance institutions. It is also important to extend the scope of
mutual cooperation and complementary activities between the research institutions of each country within
the region.
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Training on fish health management has been undertaken by a number of regional institutions. The
National Research Institute of Aquaculture in Japan willingly accepts foreign trainees and works towards
the introduction of new technologies in their countries. The Southeast Asian Fisheries Development
Center (SEAFDEC, Philippines) and the Aquatic Animal Health Research Institute (AAHRI, Thailand)
have regular training programs for regional aquaculturists and extensionists, offering courses at different
levels with different approaches addressing the specific requirements and needs of trainees and their
countries.
2.3.5. Information on diseases
A grasp of domestic/international fish disease information, based upon passive/active surveillance, is
indispensable for fish disease control; thus OIE Member Countries should exchange epidemiological
information (12, 15).
The OIE has a fish disease information system similar to that for livestock. In the Asia-Pacific region, the
OIE started to collect fish disease information through its OIE Regional Representation in Tokyo in 1998,
based on discussions during the OIE/FAO/NACA (Network of Aquaculture Centers in Asia-Pacific) joint
workshop held in 1998. This information is published and distributed on a quarterly basis.
For the above-mentioned system to function effectively, it is especially important that information on
diseases be collected accurately and sufficiently in each country. However, it is not necessarily easy to
implement, because of the differences in the socio-economical situations between countries. Each country
should thus make an effort to satisfy the following conditions:
-
each country should have sufficient diagnostic ability as well as the manpower and infrastructure to
sustain diagnostic operations; and
efficient systems should be constructed and managed to communicate information on fish diseases
(reports by responsible section).
For this system to function smoothly, it is also important for the relevant institutions to maintain regular
contact and cooperate closely with one another.
The International Database on Aquatic Animal Health was established and updated by the Centre for
Environment, Fisheries and Aquaculture Sciences (CEFAS), OIE Collaborating Centre at Weymouth
(United Kingdom). Access to this database, which can be found on the OIE Delegates' web site, is
presently restricted to the OIE Delegates. Delegates have been asked to evaluate its contents and to
compare the data from the scientific literature with the official OIE data for their respective countries.
2.3.6. Use of drugs and vaccines
Regulation on the approval and use of drugs for aquaculture has not necessarily been set up in the
countries in this region, and even if it does exists, the provisions may differ by country (35, 42).
However, drugs for aquaculture should be approved by stringent examinations, such as those used for
veterinary drugs. It is important to determine the appropriate signature/dosage and withdrawal period of
each drug.
In addition, problems relating to drug usage, similar to those encountered in the veterinary field, have
recently been reported by some countries (4, 20). Therefore, drugs should be used taking into
consideration the following points (19):
-
disease control by drugs should only be conducted after an accurate diagnosis;
those who administer drugs must be trained to understand the drug administration method;
unregulated and unrestrained drug use may cause drug residue problems, and continuous use of
antibacterial compounds can encourage tolerance to drugs; and
in order to avoid drug residue problems in fish, it is important to strictly observe the determined
conditions.
In Europe, vaccination programs have obtained good results in terms of disease control (10, 24).
However, the present number of commercially available vaccines is still limited in Asia compared with
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Europe and the United States of America (USA) (31, 42), where more than ten kinds of vaccines are
available. The conceivable reasons are that, unlike in Europe and the USA, aquaculture in Asia involves
many fish species and a considerable amount of damage is caused by crustacean diseases for which
vaccines are more difficult to develop than for finfish diseases. There are also many difficulties in
developing practical vaccines for finfish due to problems of fish handling, difficulties in evaluating
efficacy and efficacy variances between different fish species (31). Nonetheless, the use of vaccines
rather than antibacterial drugs is desirable, if it is feasible (26).
2.3.7. Legal framework
Once a potentially serious transmissible or exotic disease has invaded a country, it becomes difficult to
eradicate it and the possibility of disease establishment in the country increases (3). Since many countries
have experienced the establishment of exotic diseases, several have established legal systems for disease
control and quarantine systems such as, for instance, an import permit system, in the case of Australia,
Japan, the Republic of Korea, New Zealand and Taipei China, etc. (1).
Countries in this region should discuss effective disease prevention measures in order to establish legal
frameworks that include quarantine systems, taking into consideration scientific evidence, relations with
industry and cost effectiveness (12).
2.3.8. Topics
As mentioned earlier, one of the serious problems in this region is WSS in crustaceans (16, 17, 29, 32). In
the past, Japan has experienced outbreaks of baculoviral midgut-gland necrosis (BMN) in shrimp (27, 40,
41), but an intensive study by Dr Momoyama (Yamaguchi Prefectural Fisheries Experimental Station)
(28) has shown that disease outbreaks decreased gradually after the disinfection of facilities and washing
of the fertilized eggs. Japan has not experienced this problem since 1992 (no outbreaks of the disease
have been reported since 1992).
Presently, measures against WSS utilize basic means such as cleaning and disinfection of facilities and
equipment, disinfection of fertilized eggs and water supply or selection of specific pathogen free (SPF)
brood stocks by polymerase chain reaction (PCR) (39). In the case of WSS, investigation on these issues
has been promoted and the results are applied especially in the shrimp hatchery. Furthermore,
considerable efforts are being made on fish farms. The Japanese guidelines for shrimp farmers are
attached as a reference (Appendix 1).
2.3.9. Future needs
Every country should establish an emergency program according to its aquaculture situation to eradicate
important target diseases, such as untreatable diseases or serious exotic diseases, which could invade the
country (12).
Appropriateness of disease control measures should be investigated on a scientific basis, and risk
assessment should be implemented, if possible, prior to the establishment of emergency program.
However, as for risk assessment, knowledge of epidemiological factors, such as vectors, reservoirs or the
relationship between the pathogen and the host’s immunity, is insufficient. Therefore, each country
should promote research on aquatic animal epidemiology as well as methods of risk assessment.
In the meantime, it is difficult for countries with no occurrence of the target diseases to independently
take measures against exotic diseases or unknown diseases. Such countries should promote the
establishment of a cooperative relationship with both research institutes in countries which have
experienced the disease and the OIE to encourage training in diagnostic techniques, the distribution of
diagnostic solutions, reporting to the OIE, the implementation of measures to prevent the disease from
spreading to other countries, etc.
Furthermore, the establishment of Regional or Global Reference Laboratories and crisis management
systems (including emergency programs) is required to keep economic impact to a minimum.
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Conf. OIE 1999
3. SEA-CAUGHT FISH
According to the questionnaire results, Australia uses barramundi, prawns, molluscs, pearl oysters and native finfish for
wild stocks and natural seedlings; Japan uses yellowtail, eel, ayu (sweet fish); the Republic of Korea uses yellowtail,
and Thailand uses snakehead fish and marble goby. However, it is thought that many more species are used in
aquaculture. The problems mentioned in the questionnaire results include the appearance of latent diseases in
aquaculture facilities, the possibility that natural seedlings carry certain pathogens, and the fact that seedlings are often
kept in overcrowded compartments for extended periods of time.
Natural seedling or brood stocks are used in aquaculture when a seedling production method is not fully established or
when natural seedlings can be obtained at a lower price. However, mass mortality in wild stocks has been reported (30).
The fish species used in this case is Pilchards (Sardinops neoplichardus) but the possibility that natural seedlings or
brood stocks carry certain disease agents cannot be denied. For example, natural shrimp caught for seedling production
often carry white spot syndrome virus. As mentioned earlier, the problem is that seedlings are often kept in
overcrowded conditions for extended periods.
Therefore, seedlings producers should eliminate infected natural brood stocks, and aquaculture farmers should observe
natural seedlings, whether healthy or not, for a certain period prior to introduction into the aquaculture site. Aquaculture
farmers should use healthy seedlings.
4. RECREATIONALLY CAUGHT FISH
According to the answers submitted, no country has experienced the spread of pathogens/disease resulting from the use
of unpreserved baits for aquatic animals in recreational fishing. It therefore seems at present that there is little necessity
in giving consideration to this issue.
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Appendix 1
GUIDELINES FOR PREVENTIVE AND MANAGERIAL MEASURES AGAINST PENAEID ACUTE
VIREMIA (WHITE SPOT SYNFROME) FOR SHRIMP (PENAEUS JAPONICUS) FARMERS IN JAPAN
Shrimp farmers (hereinafter referred to as 'farmers') should take measures such as thoroughly disinfecting aquaculture
ponds (hereinafter referred to as 'ponds') that have contracted the disease. At present, this disease can not be cured by
medicine because of the viral causative agent.
The measures that will be discussed in this document can be divided roughly into three types:
Farmers
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should thoroughly eliminate the virus if the causative agent exists in the pond (§ 1);
should not allow the virus to contaminate the aquaculture area and should prevent the spread of the virus (§ 2); and
should make efforts to sustain good conditions in the aquaculture area (§ 3).
Furthermore, these measures should be carried out at the appropriate times.
1.
Disinfection of the pond
1.1.
Preparation
Farmers should take the following measures if there has been a outbreak of mass mortality due to penaeid
acute viremia:
- Remove all of the shrimp from the pond and burn or bury the removed shrimps so as to prevent the
spread of the virus.
- Remove all of the water from the pond, drying it up. Subsequently, eliminate all of the animals in the
pond (especially crustaceans) and the animals living on the embankment of the pond, or burn all of
the animals using a gas burner.
- Turn the sand in the pond upside down using a power cultivator, and expose the sand to a sufficient
amount of sunshine.
- Repair the embankment of the pond so the disinfectant does not leak out.
1.2.
Disinfectant
- It is preferable to use chlorine chemicals as a disinfectant, but attention must be paid to whether or not
the chemicals can have a serious impact on the environment.
- Other chemicals are not to be used at the same time.
1.3.
Method of disinfection
Farmers should:
- Pay close attention to the warnings described on the packages of the disinfectants.
- Put a small quantity of water into the pond and scatter the disinfectant so as to lessen the
concentration of the effective component to 0.06%.
- Turn the sand in the pond upside down using a power cultivator so the disinfectant penetrates the sand
sufficiently.
- Leave the pond as is until no free chlorine can be detected. If free chlorine is detected, the pond must
be left for a longer period of time or the chlorine must be neutralized with twice the concentration of
sodium thiosulfate.
- If shrimp or other animals die from this treatment, the remains of the dead animals should be
destroyed using fire or another measure, so that the causative agent does not spread.
- Dry up the pond again, and expose the sand sufficiently to sunlight.
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2.
Disinfection of tools, refrigerators and other material
2.1.
Disinfectant
- Farmers should use iodo chemicals, invert soap, etc.
- Iodo chemicals should be used at the effective component concentration of 0.05%. Invert soap should
be used at the effective component concentration of 0.1%.
- Other chemicals should not be used at the same time.
2.2.
Method of disinfection
- Prior to disinfection, the tools, refrigerators walls, loading platforms for the trucks, etc., should be
cleaned and all dirt removed.
- After drying the above-mentioned tools etc., disinfectant should be sprayed uniformly on them, or the
tools, etc., should be dipped in disinfectant.
- Between thirty minutes and one hour after completion of the above-mentioned measures have been
put into operation, the tools, etc., should be washed sufficiently and dried again. In addition, the tools
should be exposed to sunlight.
- These measures should be carried out simultaneously with the disinfection of the pond.
3.
Usual disease-control measures
3.1.
When seeds are used, farmers should research the history of treatment for the seed, and only sound seeds
that are not suspected to be contaminated with causative agents should be used.
3.2.
Farmers should not enter other aquaculture farms without due consideration. In particular, farmers should
be sufficiently cautious of aquaculture farm where there has been a disease outbreak.
3.3.
There should only be one entrance to the farm. Footwear or truck tires should be disinfected at the
entrance using the method of disinfection for tools, refrigerators, etc. Farmers also should disinfect their
hands with invert soap, etc.
3.4.
Farmers should periodically observe the shrimp in the pond, and when they find dead shrimp, they should
destroy them using fire or another appropriate measure.
3.5.
At the entrance of the farming management facility, footwear should be disinfected using the method of
disinfection for tools, refrigerators, etc., and farmers should disinfect their hands with invert soap. In
addition, at the farming site, clothing and gloves should not be shared among farmers, and these should
be disinfected regularly.
3.6.
Farmers should try not to use the pond for too long, and should make efforts to improve the bottom
materials.
3.7.
Farmers should pay attention to birds and other animals, because these animals may transport diseased
shrimp to the pond, thus spreading the disease.
3.8.
Farmers should always keep the area surrounding the pond and the farming management facility clean.
3.9.
Farmers should make efforts to maintain appropriate management for farming, such as ensuring the
proper density of farming shrimp.
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