SURVEILLANCE AND CONTROL OF MARINE FISH DISEASES. T. Håstein Head, Department of Fish Health, Central Veterinary Laboratory, Oslo, Norway

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1 SURVEILLANCE AND CONTROL OF MARINE FISH DISEASES T. Håstein Head, Department of Fish Health, Central Veterinary Laboratory, Oslo, Norway Original: English Summary: Some of the anatomical and immunological features of fish that distinguish them from terrestrial animals are described and information is provided on diseases of socio-economic importance in marine fish world-wide. A brief overview is given of the main disease problems in European mariculture based on information received from the Member Countries of the Office International des Epizooties. The basic components for disease surveillance in fish are given with emphasis placed on the establishment of a reporting system and a health control monitoring system. The need for a legislative framework is underlined. Examples of existing legislation are given as well as measures to be used in disease surveillance programmes for fish. Such measures include actions to be taken when a notifiable disease/disease agent is detected as well as quarantine measures, confirmatory diagnostic procedures and methods of control. There are many approaches to controlling diseases in mariculture. These include clearly defined procedures for inspection and health control in fish farms, import regulations, quarantine measures, regulations regarding the introduction of fish species into new areas, transport regulations, restrictions on fish movement, disinfection procedures, defined procedures for dealing with outbreaks of serious transmissible diseases, including eradication procedures (i.e. stamping out), sanitary slaughtering and vaccination strategies. Several on-the-farm factors which can diminish the risk of disease in marine fish farm establishments are described. These include localisation (site selection), distance between farms, health control, health certification, certification of fish transfers (transportation), division of yearclasses, isolation and sanitation in connection with disease outbreaks, regionalisation, sanitary slaughter procedures and disinfection of offal/wastewater in connection with slaughtering. Factors that improve the ability of the fish to withstand disease are also mentioned, with special emphasis on selection of disease free brood stock, disease control through genetic improvement and vaccination. Finally, the major drugs used in fish farming are listed. 1. INTRODUCTION The OIE Regional Commission for Europe has considered it opportune to discuss the topic of surveillance and control of marine fish diseases due to the increasing impact of diseases in marine fish farming in Europe. Information on diseases in mariculture has been received from Croatia, Cyprus, Denmark, Finland, Germany, Iceland, Israel, Italy, Latvia, Lithuania, the Netherlands, Norway, Poland, Slovenia, Spain, Sweden, Turkey and United Kingdom. Two of the countries reported that there was either no farming activity in their coastal waters (Lithuania) or that the waters were not recognised as marine waters (Finland). The information given is incorporated in this report. The prevalence and spread of disease problems in marine fish farming have become more and more important in recent years. As for terrestrial animals, the main disease problems in mariculture are caused by a wide range of infectious organisms, including bacteria, viruses, fungi, protozoan and metazoan parasites; nutritional and environmental problems i.e. algal blooms, do occur. The disease spectrum may vary a great deal on a global basis depending on the farming conditions, fish species and status of infectious agents in fish within different regions of the world (23). Because of space limitations, it is not possible to cover all aspects of surveillance and control of marine fishes in detail. For this reason, the disease problems reported in mariculture will only be referred to briefly without description of clinical signs and pathology. Furthermore, only the principles to be used in surveillance and control of marine fish diseases will be covered. Normally, marine fish are defined as fish species spending their entire life cycle in sea water. However, in this context, the definition has been broadened and will also to some extent cover anadromous fish species (salmonids) farmed in sea water

2 1.1. Anatomic structure of fish The anatomic features of farmed fish species used in aquaculture differ quite significantly. A few characteristics are common. All fish species have crania and backbones and their bodies are divided into a head, trunk and tail. The surface of the fish (skin) consists of an outer epidermis of living epithelial cells and mucus cells that secrete a glycoprotein-rich mucus which plays an important role in primary defence mechanisms against bacterial pathogens. The internal organs of fish are to a great extent similar to those of terrestrial animals. The haematopoietic tissue producing blood cells is situated in the kidneys in which chromaffin tissue (adrenal medullar tissue of higher vertebrates) is also present. The interrenal gland, which is involved in mineral metabolism, response to stress and the use of stored fat, is also situated within the kidneys. Contrary to terrestrial animals, the pancreas in fish is not a distinct organ, but is comprised of cells located in or around the liver/pyloric caeca. Like mammals, fish have a specific immune response system. However, differences exist between the immune system of fish and mammals. Fish lack bone marrow and lymph nodes, both important immunological organs in mammals. Instead, the thymus, kidney and spleen play an important role in the fish immune system (45). As in mammals, the predominant immunoglobulin in blood is IgM. As fish are poikilothermic, the time for development of immunity and level of response is temperature dependent (45) Disease problems Some diseases, such as classical vibriosis, furunculosis, pasteurellosis and streptococcosis are described from many countries throughout the world, while other diseases, such as cold water vibriosis, infectious haematopoietic necrosis (IHN) and viral haemorrhagic septicaemia (VHS) have a more restricted distribution. International trade in live fish and fish eggs has led to the spread of new diseases to new areas. However, increased awareness of disease risks, new health control legislation and better diagnostic methods, which have increased the ability to detect diseases and pathogens in fish, are helping to reduce the frequency of introduction and the spread of diseases (62). Tables 1, 2 and 3 show some of the major important diseases of socio-economic significance in fish farming worldwide, diseases reported in European mariculture and fish species farmed in European mariculture. 2. SURVEILLANCE There is no definition of surveillance in the OIE International Animal Health Code or in the OIE International Aquatic Animal Health Code (42,43). However, Chapter "Surveillance and monitoring" in the mammals Code (42), the "recommended Standards for epidemiological surveillance systems for rinderpest" (3) as well as the papers by Hueston (22) and Baltar (6) on surveillance and monitoring systems for animal diseases give definitions and purposes of surveillance which easily can be adopted for health control in marine fish farms. Disease surveillance in marine fish may be defined as follows: "Surveillance of marine fish means continuous examination of a given population to detect the occurrence of diseases that will be subjected to control purposes and that may be based upon random sampling and testing of the population." Disease surveillance and monitoring is necessary to obtain evidence on whether a country or a region is free from a disease or a disease agent. So that the Veterinary Services or other competent authorities may provide evidence on freedom of reportable diseases, it is necessary to have a national surveillance and control programme. Such a programme must be based upon a legislative framework. Directive 91/67/EEC of the European Union, the National Legislation in Great Britain for the control of fish diseases, the finfish health protection regulations in Canada (11) and the Norwegian aquatic animal disease legislation are examples of existing fish health protection legislation that apply to aquatic animals. It is important that any legislation give the competent authority the legal right to enforce special measures when the presence of socio-economic important diseases in the fish farming industry is suspected. These measures depend on what kind of disease is to be brought under control. Such measures may include quarantine (restrictions on movements of fish), confirmatory diagnostic work and specific control measures such as disinfection of offalls

3 Table 1 Diseases of socio-economic importance in mariculture worldwide Pathogen Host Disease Environment Virus IHN virus Atlantic salmon, Pacific salmon rainbow trout Infectious haematopoietic necrosis (IHN) Western North America, Japan, Europe, fresh water, sea water (64) VHS virus Rainbow trout, turbot, brown trout, grayling, whitefish, pike, cod, herring, Pacific salmon Viral haemorrhagic septicaemia (VHS) Europe, Pacific coast of USA and Canada, fresh water, sea water (64) VNN virus Sea bass, halibut, turbot, Japanese parrotfish, rock porgy, tiger puffer, striped jack, kelp grouper, redspotted grouper, Japanese flounder Viral encephalopathy and retinopathy (viral nervous necrosis, VNN) Europe, Japan, Australia, sea water (8, 10, 19, 21, 36, 37, 38, 39, 40, 48, 66) Bacteria Vibrio anguillarum Many fish species Classical vibriosis Worldwide, brackish water, sea water (5, 25) Vibrio salmonicida Atlantic salmon, cod Cold water vibriosis Europe, east coast of North America, sea water (5, 25) Aeromonas salmonicida atypical A. salmonicida Salmonids, Salmonids, turbot, green flounder Furunculosis Wide distribution, freshwater, sea water (5, 25, 63) Pasteurella piscicida Yellowtail, sea bass, striped bass, sea bream, red drum Pasteurellosis Freshwater, seawater (5, 25) Streptococcus spp. Many fish species Streptococcosis Freshwater, seawater (5, 14, 25) Renibacterium salmoninarum Salmonids Bacterial kidney disease (BKD) North America, Europe, fresh water, sea water (5, 25) Mycobacterium spp. Many fish species Fish "tuberculosis" Fresh water, sea water (6, 25) Piscirickettsia salmonis Atlantic salmon, Pacific salmon, rainbow trout Piscirickettsiosis Pacific coast of America, Europe, fresh water, sea water (25) Fungus Ichthyophonus hoferi Many fish species Visceral mycosis Sea water Parasites Lepeophtheirus sp., Caligus sp. Marine fish species Skin Sea water

4 Table 2 Diseases reported in European mariculture* Disease Host Country Viral diseases Viral haemorrhagic septicaemia (VHS) Rainbow trout, turbot Denmark, United Kingdom Infectious pancreatic necrosis (IPN) Atlantic salmon Norway, United Kingdom Viral nervous necrosis (VNN) Sea bass, sea bream, halibut, turbot Italy, Malta, Norway Lymphocystis Red drum, sea bass, sea bream Israel, Italy Infectious salmon anemia (ISA) Atlantic salmon Norway Bacterial diseases Cold water vibriosis (Vibrio salmonicida) Atlantic salmon, cod Iceland, Norway Vibriosis (Vibrio anguillarum) Atlantic salmon, rainbow trout, sea bass, sea bream Croatia, Denmark, Estonia, Israel, Italy, Slovenia, Winter ulcers (Vibrio viscosus) Atlantic salmon Iceland, Norway Furunculosis (Aeromonas salmonicida subspecies, Atypical A. salmonicida, motile Aeromonas spp.) Pasteurella (Pasteurella piscicida) Streptococcus infection (Streptococcus iniae) Bacterial kidney disease (BKD, Renibacterium salmoninarum) Mycobacteriosis (Mycobacterium marinus) Atlantic salmon, rainbow trout, turbot Red drum, striped bass, sea bass, sea bream Red drum Atlantic salmon Sea bream Denmark, Estonia, Iceland, Norway, Israel, Italy, Slovenia Israel Iceland, Norway Israel Epitheliocystis (Chlamydia) Sea bream Israel Parasitic infections Microsporidia, Myxosporidia sp. Sea bream Malta, Italy Diplectanum sp. Sea bass Italy Obdinum sp. Sea bream Italy Fish louse ( Lepeophtheirus spp., Caligus spp., Argulus sp.) Salmonids, mullets Norway, Italy, * Responses from OIE European Member Countries. No diseases were reported by Cyprus, Germany and Spain

5 Table 3 Fish species farmed in European mariculture Fish species Country Global production in sea water (1993)* mt Production in Europe in sea water (1993)* mt Sea bass (Dicentrarchus labrax, Dicentrarchus sp.) Croatia, Cyprus, Iceland, Israel, Italy, Malta, Spain, Turkey Striped bass (Morone saxitilis) Israel 300 Gilthead sea bream (Sparus aurata) Croatia, Cyprus, Israel, Italy, Spain, Turkey Japanese red sea bream (Pagrus major) Sheepshead brea (Puntazzo puntazzo) Red drum (Sciaenops ocellatus) Yellow tail ( Seriola quinqueradiata) Cyprus ** Cyprus 15** Israel Spain Tuna (Thunnus thynnus) Spain ,7 Mullet (Mugilidae) Italy, Spain ,9 Turbot (Psetta maxima) Halibut (Hippoglossus hippoglossus) Common sole (Solea vulgaris) Iceland, Norway, Spain, United Kingdom Iceland, Norway, United Kingdom Spain Cod (Gadus morhua) Norway Atlantic salmon (Salmo salar) Rainbow trout (Oncorhynchus mykiss) Sea trout (Salmo trutta) Whitefish (Coregonus lavaretus) Iceland, Latvia, Norway, Spain, United Kingdom Denmark, Estonia, Germany, Iceland, Norway, Sweden, United Kingdom United Kingdom Estonia European eel (Anguilla anguilla) Italy, Spain ,6 Lamprey (Lampetra fluviatilis) Latvia No figures No figures * FAO, Aquaculture production statistics, (FIDI/C815 (Rev. 7). ** Based upon figures reported by the OIE European Member Countries. The basic foundation for surveillance and monitoring leading to reliable results reflecting the true disease status of a country/region is epidemiology (22). Determination of the true disease status in a marine fish population requires both active and passive surveillance. Active surveillance includes inspections and examinations in the farms, in fish slaughterhouses as well as disease control in wild species. Passive surveillance includes laboratory reports and other collected test results from research programmes, etc. (22). To achieve this, in the best possible way, it is in my opinion preferable to have a decentralised veterinary (fish health)

6 infrastructure that is well-established and functions locally in the regions where the fish farms are located, as well as a competent laboratory system and a comprehensive, co-ordinated reporting system for the diseases of concern. The reporting system must be run by the competent authorities responsible for fish health management in marine fish farming, preferably the Veterinary Services. Carey (personal communication 1996) suggested that the essential elements for a national programme should include: disease surveillance - A mandatory reporting system for fish diseases of concern which are detected by health officers (veterinarians, biologists) or the fish farmers themselves and brought to the attention of the competent authority responsible for diseases in aquatic animals. - A national health monitoring programme with examination of susceptible species of wild and cultured stocks in order to obtain information on the occurrence of fish diseases/disease agents and/or transmission of diseases between farms/regions. Mandatory reporting of diseases/disease agents can be used as a source of information for the health monitoring programme. - A competent laboratory service carrying out diagnostic work using quality assured procedures which back up the field health service. - An established national/regional database for disease recording that can be used to identify and maintain disease free zones. - A register of fish farms in operation on a national level. - A legislative authority to undertake emergency disease control measures. Coupled with this authority is a requirement for governments to identify compensation mechanisms for affected fish farms. Surveillance implies that official action will follow if a notifiable disease or infectious agent is detected, while the gathering of information on non reportable diseases /agents discovered through routine diagnostic service in the fish farms must be reported by the responsible fish health officer(s) or even by the fish farmers themselves (3,22). An overall approach to fish health surveillance in fish farms is laid down in the OIE Diagnostic Manual for Aquatic Animal Diseases (43). This approach must be based upon: - Assessments of health status in a production site for marine fish based on regular inspections, standardised sampling procedures and laboratory examinations according to instructions given in the OIE Manual or other quality assured methods described elsewhere. - Stocking fish in marine sites with only material showing acceptable health standards. - Eradication procedures for diseases whenever possible. In this respect it is not only necessary to investigate any situation where fish exhibit clinical signs of disease, but also to carry out examinations when fish appear clinically normal. For some viral diseases reported in marine fish species, such as VHS, it is possible to establish laboratory procedures that may reveal a latent carrier status whereas for others, such as VNN, it is so far not possible. For many bacterial diseases, it is sometimes also impossible to detect latent carriers. This has been experienced with furunculosis in salmonids. More frequent testing over the years, may, however, increase the possibility of detecting such diseases in the carrier state. The number of fish to be examined will vary depending upon whether clinical disease testing or screening for carrier fish is conducted. The OIE Diagnostic Manual (43) gives indications for the numbers to be examined as well as sampling specifications according to the objectives of a given fish surveillance programme. Although the Manual states that the achievement of health status of a fish population in a specific farm/site should be based on twice yearly inspections at the appropriate lifestage of the fish and at the time when it is most likely that the diseases in question could be detected, it is my opinion that inspections and examinations should be more frequent. With an established decentralised fish health service working in close cooperation with appropriate competent diagnostic laboratories and the official Veterinary Service (competent authority), inspections should ideally be carried out on a monthly basis with at least two inspections being carried out by the official service. During these inspections, examinations of fish showing abnormalities, abnormal behaviour or other clinical signs of disease should be carried out and relevant samples sent for laboratory testing. Furthermore, all documents on fish mortality, fish origin, etc., should be examined in order to ensure that the farm in question complies with all official regulations and policies. This implies that the farms must keep registers on defined information of importance for the maintenance and surveillance of the fish health in the farm

7 In addition to the "on site" examinations of fish, routine examinations should ideally also be carried out in connection with the slaughtering of the fish for consumption, similar to the meat inspection systems for poultry and terrestrial animals. It is important to supplement information on diseases of concern from fish farms with surveys of diseases in wild populations. Feral and cultured fish are susceptible to the same diseases, and information from wild populations provides essential data for epidemiological studies (55). Determination of true disease status in a marine fish population requires, as previously mentioned, both active and passive surveillance. Based on the health surveys carried out on farms by competent personnel, reports from fish slaughterhouses during slaughtering and other documentation accumulated through existing programmes such as diagnostic laboratory records, Veterinary Services (competent authority) should be able to provide information on the disease situation in marine farms and enable effective decision-making for the control of diseases of importance (22). Ideally, one should be able to screen for all socio-economically important diseases reported in marine fish species; however, the minimum requirement should be screening/monitoring for the diseases listed in the OIE International Aquatic Animal Health Code (43) and other major serious diseases that affect marine fish species in a given country. If financial resources for surveillance and monitoring are limited (as they usually are), then such work should concentrate on frequent inspections and examinations of material from marine fish hatcheries, brood fish establishments and breeding stations (where they exist) and fewer inspections in "on growing" farms should be carried out. 3. CONTROL All disease control in animals, whether terrestrial or aquatic, starts with a good legal framework (11, 23) which can be used as a tool to avoid the introduction and spread of serious fish diseases that are of socio-economic importance. Once a disease has become established in a free-living fish population or under farm conditions, the possibility of it subsequently spreading to other farms via water or transfer of fish by trade poses a permanent risk to the fish farming industry as well as to wild fish resources (23). Legislative measures must therefore include regulatory control in order to avoid the introduction of serious transmissible diseases into and within a country. A wide range of steps may be taken such as: - Clearly defined procedures for inspection and health control in fish farms - Import regulations - Quarantine measures - Regulations regarding the introduction of new fish species into new areas - Transport regulations - Restrictions on movement of fish - Disinfection procedures - Defined procedures for dealing with outbreaks of serious transmissible diseases, including eradication procedures (i.e. stamping out), sanitary slaughtering, etc. - Vaccination strategies. Even where a good legislative framework may exists, disease problems will occur from time to time and it is important to bear in mind that disease control by prevention is preferable to medical treatment. It is important to maximise the ability of cultured fish in mariculture to withstand disease as well as to minimise their exposure to pathogens, thus diminishing the risk of disease outbreaks. This is of course extremely difficult to achieve in floating cages in sea water, because of the free exchange of water (and water-borne pathogens) between fish cages and the surrounding sea water. In addition to a legal framework for disease control management, several on-the-farm factors are of great significance for the achievement of disease prevention. These include: - Site selection - Distance between farms - Health control and certification - Certification of transports - Division of yearclasses - Isolation and sanitation in connection with disease outbreaks - Regionalisation - Sanitary slaughter procedures - Disinfection/destruction of offal Fish farm control measures Site selection

8 A fish farm should ideally be located and organised in such a way that the risk of introducing pathogens into the facility is minimised. This means that the farms should preferably either be landbased or, if located in sea water, isolated and at a sufficient distance from other fish farms/fish slaughterhouses etc., to avoid waterborne spread of infectious agents. Experience from Norway has shown that A. salmonicida may be disseminated over distances of more than 2 km in sea water. Furthermore, epidemiological studies (26) have shown that the risk of contracting infectious salmon anaemia (ISA) from an adjacent farm is twice as high if the distance is less than 5 km. Fish farms in shallow waters may also be at higher risk for disease outbreaks than are fish farms in more open coastal areas. Alternative sites should also be available in order to separate age groups and thus fulfil the "all in - all out" principle Water treatment It is not always possible to obtain ideal water quality in marine farms as this depends on the quality of the marine water supply surrounding the farms; less than perfect conditions must thus be accepted. The water supply to marine fish hatcheries and landbased fish farms should, however, be disinfected prior to use in order to prevent waterborne infections into such farms. The technology needed to optimise factors such as oxygenation, degassing of harmful gases dissolved in the water (e.g. nitrogen gas supersaturation), temperature control, disinfection etc. by means of aeration devices, filtering systems, heat pumps, UV disinfection etc. is available. Disinfection of the water supply as well as the effluent water in marine fish hatcheries landbased farms is an effective means of disease control, as are the disinfection regulations regarding offal and discharge water from fish slaughterhouses and production facilities, as well as transport vehicles (trucks, wellboats etc.) (49, 59). Possible methods for disinfection include heating, ozonization, chlorination and UV radiation. With the current cage technology for farming in the marine environment, it is not possible to implement the same type of water treatment, but "fencing off" the cages or moving the farm onshore could be a way of reducing the disease risk by water Fish culture In addition to optimal environmental criteria to reduce stress-induced disease factors through localisation and water quality criteria, other important factors are: - Optimal fish density to avoid crowding stress. It is not possible, however, to establish exact density figures due to the influence of several factors such as water quality, fish condition etc. - Reduction or elimination of handling or other stress. If fish are unavoidably stressed, i.e. during sorting and/or transportation, they must be given enough time to recover before being subjected to further stress. - A systematic programme for health control may also prevent serious outbreaks of disease and thus prevent the introduction or inadvertent transfer of disease between fish farms, to wild stocks or vice versa (11). In this respect it is also necessary to know the disease status of wild populations, as wild marine fish material are often introduced to marine fish enterprises (56). An effective health control programme involving regular professional inspection and diagnostic work is of great importance in this respect, as are regionalisation and fish transfer restrictions. - Disinfection of eggs prior to introduction into hatcheries (9,54). - Prophylactic control of disease by means of vaccination programmes are one of the most important effective preventive measures to control serious infectious diseases of socio-economic importance because of fish mortalities and increased cost due to medication. - Separation of yearclasses. Here, ideally the "all in-all out" principle should be followed. There is an increased understanding and acceptance for this principle among fish farmers although it is still difficult to achieve. - Selection of disease free brood stock. This can be achieved by a continuous disease surveillance programme in the fish farms (39). - Disease control through genetic improvement. Genetic differences in disease resistance have been determined for several diseases both between and within species, but sometimes when better resistance is achieved against one disease, the same fish show a lesser degree of resistance to another

9 disease. An effective method for measuring disease resistance has still not been fully developed and survival studies are still the only selection criteria used (47). Development of indirect parameters of the immune system as selection criteria, such as lysozym and complement activity, is currently under way and will be used in future work (34). The development of gene mapping and genetic markers in aquaculture will probably help to eliminate defects and "disease" genes and to increase resistance (55). - Disease control through nutrition. Any impaired nutritional condition will contribute to reduction in disease resistance at any stage in a fish s life. Correct nutritional management is thus also a vital factor in controlling diseases in fish (29,52). It is generally accepted in Norway that impaired nutritional status may have an influence on the mortality of halibut larvae suffering from VNN Vaccination Correct use of effective vaccines is one of the most important tools in the organised control of the serious infectious diseases in marine fish species. In this respect there is a need for ongoing research concerning the following: - Improvement of existing vaccines - Improvement of vaccine delivery methods - Correct use of vaccines. The term vaccinology has been introduced as a scientific term for this field. Vaccines for fish must be defined as biologics and should be approved by the competent authority of a country. Approval of a vaccine on a general basis, however, may not mean that it should be approved for general use, as such approval will be dependent upon the disease situation and the vaccination strategy to be followed in a country, as decided by the competent authority responsible for disease control in aquatic animals. Vaccines should only be allowed to control diseases which are widespread in a region or a country, i.e. furunculosis, cold water vibriosis, classical vibriosis, pasteurellosis, streptococcosis, yersiniosis etc. Serious viral diseases such as VHS, IHN, ISA, which have limited distribution, should preferably be controlled by other means, such as stamping out procedures, sanitary slaughtering followed by disinfection and fallowing of a site for a certain period. One of the important advantages of vaccination against widespread bacterial diseases is the reduction in the use of antimicrobials (20, 34). Figures 1 and 2 show the decline in the use of drugs in Norwegian fish farming due to vaccination and improved management. Today, vaccines against many of the most important fish diseases, including furunculosis, coldwater vibriosis, classical vibriosis, yersiniosis, etc. are commercially available and continuos research is being conducted to improve the effectiveness of the vaccines (1, 15, 16, 17, 27, 28, 57, 58, 60). A vaccine against IPN, a viral disease in several marine fish species, seems to be effective in reducing disease problems in Atlantic salmon in Norway. (13,15) Currently, intensive research is under way in order to come up with effective vaccines against pasteurellosis (30, 50, 60) and streptococcosis (18, 53) in marine fish species farmed in southern Europe. Investigations have also begun on vaccines against certain parasitic (65) and viral diseases (33, 62). However, as previously mentioned, vaccination against viral diseases might not be the best strategy to follow. Information on correct use and economic benefits from vaccination is also important (31). There are, however, several aspects to be considered in connection with vaccination (23, 32, 51). These are: - The disease to be vaccinated against - Method of vaccination (dip, bath, injection) - Vaccination time, single vaccination/re-vaccination/temperature at vaccination. Figure 1*

10 kg Sales figures, in kilogrammes active substance, antibacterial drugs used in salmonid farming in Norway Year Florfenicol Flumequine Furazolidone Oxolinic acid Oxytetracycline Trimeth/sulphadiaz. * Grave & Markestad, 1996 Figure 2* Number of treatments per kg farmed salmonids versus sales figures, in litre (x 100), of vaccines against furunculosis Number of treatments 0,7 0,6 0,5 0,4 0,3 0,2 0, Year Litre (x1000) vaccine sold Antibacterial drugs a Immersion b Injection c Injection oil adjuvant * Grave & Markestad, Medical treatment

11 Sometimes it may be essential to carry out medical treatment in order to control outbreaks of bacterial disease conditions for which vaccines are not yet available. Many different drugs may be used (4, 24). However, the intensive use of drugs in fish farming has potential hazards and side effects that have been brought into focus in recent years. Thus, legal constraints on the supply and use of veterinary drugs now exist in many countries throughout the world and vary from strict to lax (2). Table 4 show the major drugs used in fish farming today. Table 4 Major drugs used in fish farming* Drug Administration Indication Ampicillin Oral Bacterial infections Oxytetracycline Oral/bath/injection Bacterial infections Chloramphenicol Oral/bath/injection Bacterial infections Erythromycin Oral/injection Bacterial kidney disease Sulphonamides Oral Bacterial infections Potensiated sulphonamides Oral Bacterial infections Furazolidone Oral/bath Bacterial infections Oxolinic acid Oral Bacterial infections Flumequine Oral Bacterial infections Nuvan R Bath Salmon lice Neguvon R Bath Salmon lice Salmosan R Bath Salmon lice Formalin Bath External protozoan parasites Praziquantel (Droncit R ) Oral Cestodes Piscipar R Oral Cestodes Panacur vet. R "Hoechst" Oral Cestodes Valbazen vet. R "Smith Kline Beecham" Oral Cestodes * Reported use in marine species in Europe The serious side effects of medication, such as development of resistance, environmental effects and residual constraints, are well known and will not be dealt with here Other control measures In addition to prophylactic measures and curative medical treatment, there is also a wide range of control measures that can be undertaken, such as sampling and destruction of dead fish on the farm, disinfection of waste water/bleeding water and offall in connection with the on the farm slaughtering process or in fish slaughterhouses, disinfection of wellboats, lorries etc. The reduction and control of ISA in Norway using such measurements is a good example of disease control. Farm hygiene is also of great importance and disease control precautions should include disinfection of tanks, cages, equipment etc. as well as attention to personal hygiene and working procedures, and disinfection of footwear as well as other personal belongings that might contribute to the spread of disease (23)

12 Some countries such as Norway have established a good system for such procedures in order to prevent the spread of communicable diseases. For countries lacking the necessary legal framework for disease control in fish farming, the OIE International Aquatic Animal Health Code and Diagnostic Manual for Aquatic Animal Diseases (43) may be used as guidelines until specific legislation has been established. REFERENCES 1. Akhlaghi M., Munday B.L. & Quentel C. (1996). Passive immunisation against vibriosis parenteral, oral and immersion routes. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Alderman D.J. & Michel C. (1992). Chemotherapy in Aquaculture today. In Chemotherapy in Aquaculture: From theory to reality. ISBN Eds. Alderman D.J. & Michel C Anon (1993). Recommended Standards for Epidemiological Surveillance of Rinderpest. Re-issued June Previously entitled: Report of the Expert Consultation on Rinderpest Surveillance Systems, Paris, August Austin, B. (1988). Chemotherapy of bacterial diseases of salmonids. Proceedings. Aquaculture International Congress and Exposition, Vancouver, British Columbia Austin B. & Austin D.A. (1993). Bacterial Fish Pathogens. Diseases in Farmed and Wild Fish. Second Edition. Ellis Horwood, 384 pp. 6. Baltar J. (1994). Surveillance and monitoring systems for animal diseases. OIE Comprehensive reports on technical items presented to the International Committee or to Regional Commissions, Baptista C., Romalde J.L. & Toranzo A. E. (1996). First occurrence of pasteurellosis in Portugal affecting gilthead sea bream (Sparus auratus). Bulletin of the European Association of Fish Pathologists. 16 (3), Bellance R. and Gallet de Saint-Aurin D. (1988). L encéphalite virale du loup de mer. Caraibes Medical, Bergh Ø. & Jelmert A. (1996). Iodophor Disinfection of Eggs of Atlantic Halibut. Journal of Aquatic Animal Health, 8: Bloch B., Gravningen K. and Larsen J.L. (1991). Encephalo-myelitis among turbot associated with a picornaviruslike agent. Diseases of Aquatic Organisms, 10, Carey T.G. & Pritchard G.I. (1995). Fish Health Protection: A Strategic Role in Canadian Fisheries Management. North American Journal of Fisheries Management, 15, Chang P. H. & Plumb J.A. (1996). Histopathology of experimental Streptococcus sp. infection in tilapia, Oreochromis niloticus (L.) and channel catfish, Ictaluris punctatus (Rafinesque). Journal of Fish Diseases, 19, Christie K. E. (1996). Immunisation with viral and parasitic antigens: Infectious pancreatic necrosis. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Domenech A., Fernandez-Garayzabal J.F., Pascual C., Garcia J.A., Cutuli M.T. Moreno M.A., Collins M.D. & Dominguez L. (1996). Streptococcus in cultured turbot Scophthalmus maximus (L), associated with Streptococcus parauberis. Journal of Fish Diseases.19, Frost P., Ness A., Maaseide N.P., Knapskog D.H. & Rødseth O.M. (1996). Efficacy of a recombinant vaccine against infectious pancreatic necrosis in Atlantic salmon post-smolt. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Gatta P.P., Giorgetti G., Salati F., Ceschia G., Mazzolini, D Alterio N. (1996). Efficacy test with some oral Vibrio anguillarum vaccination trials in sea bass (Diccentrarchus labrax). Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway,

13 17. Giorgetti G., Gatta P.P., Ceschia G., Mazzolini E., Testi S., Van Duffel H. (1996). Protection of sea bass (Dicentrarchus labrax) orally vaccinated with Vibrio anguillarum. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Ghittino C. Bercovier H. & Eldar A. (1996). Immunisation with bacterial antigens: Infections with Streptococci and related organisms. Abstracts. International Symposium on Vaccinology, Oslo, Norway, Glazebrook J.S., Heasman M.P. and De Beer S.W. (1990). Picorna-like viral particles associated with mass mortalities in larval barramundi, Lates calcarifer Bloch. Journal of Fish Diseases, 13, Grave K., Markestad A. & Bangen M. (1996). Comparison in prescribing patterns of antibacterial drugs in salmonid farming in Norway during the periods and Journal of Veterinary Pharmacology and Therapy, 19, Grotmol S., Totland G.K., Kvellestad A., Fjell K. and Olsen A.B. (1995). Mass mortality of larval and juvenile hatchery-reared halibut (Hippoglossus hippoglossus L.) assosiated with the presence of virus-like particles in vacuolated lesions in the central nervous system and retina. Bulletin of the European. Association of Fish Pathologists, 15 (5), Hueston W. D. (1993). Assessment of national systems for the surveillance and monitoring of animal health. Rev. sci. tech. Off. int. Epiz., 12 (4), Håstein T. (1988). Disease Control through Management Practices. Congress Proceedings, Aquaculture International Congress & Exposition. Vancouver, British Columbia, Canada, Håstein T. (1994). Disease problems, use of drugs, resistance problems and preventive measures in fish farming world wide. Proceedings of the first International Symposium on Sustainable Fish Farming, Oslo, Norway, AA. Balkema, Rotterdam, Brookfield, eds. Reinertsen H. & Haaland H., Inglis V., Roberts R.J. & Bromage N.R. (1993). Bacterial diseases of fish. Blackwell Scientific Publications, 312 pp. 26. Jarp, J. & Karlsen, E. (1993). Risk factors for infectious salmon anemia (ISA) in sea cultured Atlantic salmon, Salmo salar L. In press. 27. Joosten E., Caumartin-Dhieux C., Vanuiswinkel W. & Romout J. (1996). Oral vaccination of fish against Vibrio anguillarum with microparticles. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Karunasager I., Otta S.K. Ali A. & Karunasagar I. (1996). Immunisation with bacterial antigens: Infections with bacterial antigens: Infections with motile aeromonads. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Lall Santosh, P. (1988). Disease Control through Nutrition. Proceedings, Aquaculture International Congress and Exposition, Vancouver, British Columbia, Canada, Laval A., Ganne V., Aucoutur J., Crespeau F. & Levy D. (1996). Efficacy and safety of new ajduvanted vaccine formulations containing Pasteurella antigens. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Leira H.L. & Baalsrud K.J. (1996). Operator safety during injection-vaccination of fish. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Lillehaug A. (1996). Vaccination strategies in seawater cage culture of salmonids. Abstracts International Symposium on Fish Vaccinology, Oslo, Norway, Lorenzen N. & Olesen N.J. (1996). Immunisation with viral and parasitic antigens. Viral haemorrhagic septicaemia. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway,

14 34. Lund, T., Fjalestad, K., Røed, K.H. & Strømsheim, A. (1992). Use of immune - parametres for indirect selection of increased disease resistance. (In Norwegian) Norsk Fiskeoppdrett, No 11A, Markestad A. & Grave K. (1996). Reduction of antibacterial drug use in Norwegian fish farming due to vaccination. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Mori K., Nakai T., Nagahara M., Muroga K., Mekuchi T. and Kanno T. (1991). A viral disease in hatchery-reared larvae and juvenile of redspotted grouper. Gyobyo Kenkyu, 26, Munday B.L., Langdon J.S., Hyatt A. and Humphery J.D. (1992). Mass mortality associated with a viral-induced vaculating encephalopathy and retinopathy of larval and juvenile barramundi. Lates calcarifer Bloch. Aquaculture, 103, Munday B.L., Nakai T. and Nguyen H.D. (1994). Antigenic relationship of the picorna-like virus of larval barramundi, Lates calcarifer Bloch to the nodavirus of larval striped jack, Pseudocaranx dentex (Bloch & Schneider). Australian Veterinary Journal, 71 (11), Mushiake K., Nishizawa T., Nakai T., Furusawa I. and Muroga K. (1994). Control of VNN in Striped Jack: Selection of Spawners Based on the Detection of SJNNV Gene by Polymerase Chain Reaction (PCR). Fish Pathology, 29(3), Nakai T., Nishizawa K, Mushiake K. and Muroga K. (1995). Control of Viral Nervous Necrosis (VNN) in Striped Jack Pseudocaranx dentex larvae. In Proceedings of Larvi 95, p 507. E.A.S. special publication, 24. Lavens P., Jaspers E. and Roelants I. (Eds. ). Gent, Belgium. 41. Nguyen H.D., Mekuchi T., Imura K., Nakai T., Nishizawa T. and Muroga K. (1994). Occurrence of Viral Nervous Necrosis (VNN) in Hatchery-Reared Juvenile Japanese Flounder Paralichthys olivaceus. Fisheries Science, 60(5), OIE International Animal Health Code (1992), Updates 1993 & OIE International Aquatic Animal Health Code and Diagnostic Manual for Aquatic Animal Diseases (1995). 44. Pedersen K., Kofoed H., Dalsgaard I. & Larsen J.L. (1994). Isolation of oxidase-negative Aeromonas salmonicida from diseased turbot Scophthalmus maximus. Diseases of Aquatic Organisms, 18: Press C..McL. & Lillehaug A. (1995). Vaccination in European salmonid aquaculture: A review of practices and prospects. British Veterinary Journal, 151, Preventing the spread of aquatic animal diseases. OIE Scientific and Technical Review 1996,15, 1-4.Eds Hill B., Håstein T. 47. Refsti, T. (1988). Disease Control through genetics. Proceedings, Aquaculture, International Congress and Exposition. Vancouver, British Columbia, Canada, Renault T., Haffner Ph., Baudin Laurencin F., Breuil G. and Bonami J.R. (1991). Mass mortalities in hatcheryreared sea bass (Lates calcarifer) larvae associated with the presence in the brain and retina of virus-like particles. Bulletin of the European Association of Fish Pathologists. 11, Rivas C., Bandin I., Cepada C. & Dopazo C.P. (1994). Efficacy of Chemical Disinfectants against Turbot Aquareovirus. Applied Environmental Microbiology Romalde J.L. & Magarunos B. (1996). Immunisation with bacterial antigens: Pasteurellosis. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Rødseth O.M. & Knapskog D. (1996). Vaccination strategies for marine cultures species. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Rørvik, K.A. & Thomassen, M. (1992). Effect of iron and omega 3 in the feed on the resistance of Atlantic salmon against disease. (In Norwegian). Norsk Fiskeoppdrett, No 11A,

15 53. Sakai M. (1996). Efficacy of β-haemolytic streptococcal vaccine in rainbow trout, Oncorhynchus mykiss. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Salvesen I & Vadstein O. (1995). Surface disinfection of eggs from marine fish: Evaluation of four chemicals. Aquaculture International, 3, Santos M.J. (1996). Observations on the parasite fauna of wild sea bass (Dicentrarchus labrax L.) from Portugal. Bulletin of the European Association of Fish Pathologists. 16 (3), Slettan, A. (1995). Isolation, characterisation and genetic analysis of simple sequence polymorphism in Atlantic salmon (Salmo salar). Thesis for the degree of Doctor scientiarum. Norwegian College of Veterinary Medicine. 57. Smith P. (1996). Immunization with bacterial antigens; Piscirickettsiosis. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Toranzo A.E., Santos Y. & Barja J.L. (1996). Immunization with bacterial antigens: Vibrio infections. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Torgersen Y. & Håstein T. (1995). Disinfection in aquaculture. Rev. sci. tech. Off Int. Epiz. 14 (2), Vigneulle M., Gravningen K. & Abiven A. (1996). Vaccination of sea bass (Dicentrarchus labrax) against pasteurellosis and vibriosis: Comparison of different vaccines. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Winton J. (1996). Immunisation of viral and parasitic antigens. Infections haematopoietic necrosis. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Winton J.R. (1991). Recent advances in detection and control of infectious hematopoietic necrosis virus in aquaculture. Annual Review of Fish Diseases. 63 Whittington R.J., Djordjevic S.P., Carson J. & Callinan R.B. (1995). Restriction endonuclease analysis of atypical Aeromonas salmonicida isolates from goldfish Carrasius auratus, silver perch Bidyanus bidyanus, and greenback flounder Rhombosolea tapirina in Australia. Diseases of Aquatic Organisms, 22: , Wolf K. (1988). Fish viruses and fish viral diseases. Cornell University Press, ISBN , 476 pp. 65. Woo P.T.K (1996). Immunisation of Oncorhynchus mykiss against the pathogenic haemoflagellate, Cryptobia salmocitica. Abstracts, International Symposium on Fish Vaccinology, Oslo, Norway, Yoshikoshi K and Inoue K. (1990). Viral nervous necrosis in hatchery-reared larvae and juveniles of Japanese parrot-fish, Oplegnathus fasciatus (Temminck & Schlegel). Journal of Fish Diseases. 13,