WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2012 33 salmon production for consumers. For broodfish, the seawater phase is longer, approximately 2.5 years, and the fish are reallocated to freshwater for some months before spawning. Slaughtering is the last stage in production; the introduction of fish pathogens to slaughterhouses is of minor importance to the aim of bioexclusion during production. Nonetheless, slaughterhouses may pose a significant risk of spread of pathogens to the surroundings (Jarp and Karlsen 1997) from receiving wellboats with fish ready for slaughter, keeping fish in waiting cages, and releasing effluents. Hygienic treatment systems for waste and process water are mandatory to reduce the risk of spread of pathogens to the surrounding environment to a minimum. The implementation of HACCP principles to these parts of the industry is of importance to food safety. Infectious agents can be introduced to a fish farm via different routes: • Live biological material – eggs or live fish, • Water (freshwater or seawater), • Wild fish (and escapees), which contribute to the water being a route of infection, • Feed, and • Vectors, which can be live creatures or dead objects, also called fomites. Vectors include working staff, servicemen, consultants, authority representatives, veterinarians, vaccination personnel, and visitors (Aldrin et al. 2010). Equipment, such as different technical installations, brushes, landing nets, and automatic vaccination machines, can carry pathogens between sites/farms, as well as transport vehicles like cars and vessels, and their cargo. Predators and scavengers (birds and animals) can also be vectors for fish disease agents (Johnson and Paull 2011). In the following discussion, potential routes of entry for pathogens will be listed and categorized according to severity as high, moderate, low, and negligible. The biosecurity plan at a fish farm must be based on the particular production system, adjusted to meet the requirements of the technical equipment and water supply of the farm, and to the disease panorama in the region. In the following discussion, typical production systems for Atlantic salmon in Norway are described. Hatchery — Smolt Farm From a biosecurity perspective, the important feature of smolt production is that housing is typically an industrial type of building (e.g., warehouse) situated close to the sea. Fry are kept in tanks, freshwater supply usually being a surface water source, often a river, but it may be a dam or a lake. Some smolt farms may use water from a well, which can be drilled to access groundwater. Supplemental seawater may be used during smolt production as a buffer to improve water quality, to increase temperature, or to acclimatize smolts to higher salinity. When fry approach smolt size, they are often moved to large outdoor tanks. Smolt production is based on fertilized eggs brought in before hatching from specialized breeding stations. Commercially available dry pellets are the only option for feeding. Fertilized eyed eggs from specialized broodfish producers are considered of generally low risk. In Norway, disinfection of eggs immediately after fertilization (Wagner et al. 2010) is mandatory by law. Disinfection may be repeated before delivery. Health control is also mandatory; for broodfish production, strengthened control is required. In general, the water supply is considered to constitute the greatest risk for introduction of pathogens to a smolt farm. The risk level varies significantly with type of water source, depending on the fish populations inhabiting the water. There is no fish in groundwater, while rivers and lakes have populations of various species. In river systems where salmonids migrate, as well as in seawater, most pathogens of importance to salmon farming may be present. The risk may be reduced significantly by employing water disinfection systems, treatment with UV light or ozone are the methods of choice (Kasai et al. 2002). However, no water treatment systems have the capacity to eliminate microorganisms completely, only to reduce the infectious load substantially (Liltved et al. 1995). Disinfection of water is mandatory when the water source contains anadromous fish and when seawater is supplemented. Logging of disinfection systems is needed to verify the effect and operation of such systems. Recycling of freshwater reduces the volume needed for supplementation, reducing the risk of introducing pathogens further and increasing the possibility to disinfect effectively the relatively lower volumes of water taken in. The number of pathogens potentially present is significantly greater in seawater than in freshwater, the reservoirs often being marine inhabitants (Johansen et al. 2011). The risk of pathogen entry is, therefore, much greater with seawater, even after treatment. Furthermore, when a smolt farm is situated on the shore, seawater may find its ways to the tanks outside the water supply; for instance, with vectors, or with sea spray during storms to outdoor tanks. Vectors may carry pathogenic microorganisms passively into a fish farm. This implies that potential vectors must have been previously in contact with infectious material, i.e. with water, other fish farms, or wild fish. Vectors are not considered to pose a major threat to smolt farm biosecurity. Yet it is of great importance to establish strict routines for hygienic control of all kinds of traffic into a fish farm area to minimize the risk. The smolt farm area should be demarcated from the surroundings by fences and outer walls of buildings, and further subdivided into areas for personnel only, various storerooms and technical rooms, as well as rooms for fish tanks. All entrances should have doors or ports that can be locked. Smolt farms situated at the shoreline will usually have a (CONTINUED ON PAGE 32) Vectors include working staff, servicemen, consultants, authority representatives, veterinarians, vaccination personnel, and visitors. Equipment, such as different technical installations, brushes, landing nets, and automatic vaccination machines, can carry pathogens between sites/farms, as well as transport vehicles like cars and vessels, and their cargo. Predators and scavengers (birds and animals) can also be vectors for fish disease agents.
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