WWW.WAS.ORG • WORLD AQUACULTURE • DECEMBER 2012 35 (CONTINUED ON PAGE 34) • Results from surveillance and screening testing of the population for selected pathogens. The smolt population, and even on-growers in sea and broodfish, may be subject to running surveillance for pathogens of particular importance. Surveillance does not, of course, prevent the introduction of pathogens, but early identification of pathogens prevents further spread and pinpoints the time of introduction, making it possible to identify the source of infection and preventing subsequent repetition. The choice of transport method to the sea-site is essential. Using tank trucks is very safe from a biosecurity viewpoint, while well-boat transport may increase the risk of being infected significantly. This risk will depend on the epidemiological status of the waters that have to be crossed. In addition to smolts, live cleaner fish for sea lice control are also introduced to a site. There are no proven cases of cross infection from wrasse to salmon. Nonetheless, a role as vector or latently infected host of salmonid infections cannot be ruled out. Import of wrasse from other regions should be avoided, if possible. In general, the number of deliveries of live fish to a site should be as low as possible, each transport or delivery contributing to an increased risk (Jarp and Karlsen 1997). Supplementing live fish during the growth period, as well as adding fish from different sites should be avoided. Together with smolts, a waterborne route of infection is the most important source of pathogens. This includes infections carried by wild fish and escapees. Wild fish and water currents cannot be controlled. This underlines the importance of biosecurity thinking when site location is chosen. Factors of importance are distance to other sea-sites (Kristoffersen et al. 2009) and other installations, such as a fish slaughterhouse (Jarp and Karlsen 1997). Other factors are depth of the sea and direction and strength of water currents, which determines effective distance to other installations. The presence of wild fish populations, particularly anadromous salmonids, is also regarded as a risk factor (Johansen et al. 2011). Once a sea-site is chosen, little can be done to control waterborne infections. Even so, coordinated production within a zone can lift the unit of concern to a higher level – to the zone. Zonal production plans include using only one year-class of fish in the zone, coordinating sea transfer and harvesting of fish, and fallowing of the zone. There should be a long distance between zones of different generations and for sailing routes for well boats. Service teams should work only for sites within the zone. The potential vectors dealt with for smolt farms – cars, trucks, cargo, equipment and visitors – should be handled in the same way and considered to be at approximately the same risk level, even in sea farms. A vector of particular interest to sea-sites is the well boat, which may contribute to the spread of infections in different ways (Murray et al. 2002). Well boats represent a very convenient way to transport live fish long distances in seawater. Fish are kept in one or more wells, which constitute most of the volume of the vessel. Ambient seawater is taken in through valves forward beneath the waterline, circulates in the well, and drains aft. Well boats are also used for other transport contracts, particularly transport of market-size fish to slaughterhouses. They may also be used in non-transport missions, like medicinal bath treatment of fish at sea farms against sea lice. The biosecurity risks connected to well-boat transport include the exposure of smolts in tanks to infectious agents in the waters along the transport route, spread of infections with live fish material, both by moving fish to new sites and new regions, and discharge of pathogens along the transport route. Cross-infection between fish groups is an issue, particularly when fish to the slaughterhouse are transported prior to transport of smolts. Risk management measures which can be applied to well boat transport, include: • Routing of such transports to shipping lanes distant to aquaculture activities, • Closing valves for water exchange when passing through high-risk areas, • Dedicating a boat to one category of fish and/or to one particular geographical region to limit risk of spread of infections, and • Disinfection of well boats between each contract or mission must be done. Effective disinfection may be difficult in such a complicated construction, particularly in older vessels that have been retrofitted from other uses. Modern well boats, built specifically for this purpose, have surfaces that can be cleaned and decontaminated more effectively. Some new well boats even have UV systems to disinfect influent or effluent water, which can be used in combination with closed valves, recycling and taking in only small amounts of water. Vectors with a potentially increased risk to sea-farms include cargo vessels, service boats and also service personnel, who arrive with service boats. Ships delivering feed will typically call at different sea-sites. There are no known examples of spread of infections with such traffic, but these vessels must be considered to constitute a risk. Delivery of feed and other cargo should be based on procedures that avoid contact with potentially infected material, and include procedures for disinfection, if such contact is unavoidable. Vessels delivering feed should not be allowed to take any type of goods in return, like wrapping. Ballast water also represents a risk (David and Gollasch 2008) and ballast tanks should not be filled or emptied closer than 5 km from any aquaculture activity. Service boats and service personnel (e.g., net cleaners) have a higher risk because of inevitable contact with material that must be considered contaminated and their work at different sites. To some extent, these judgments also apply to divers. SOPs including rules for quarantine between jobs, cleaning and disinfection procedures for vessel, equipment, and personnel are of great importance. Predators and scavengers have easier access to a sea-site than a smolt farm, and other animals may constitute a risk, such as 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.
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