Disease interaction and pathogens exchange between wild and farmed fish populations with special reference to Norway (original) (raw)
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Low-level pathogen transmission from wild to farmed salmonids in a flow-through fish farm
Acta Veterinaria Hungarica, 2021
While the potential effects of pathogens spread from farmed fish to wild populations have frequently been studied, evidence for the transmission of parasites from wild to farmed fish is scarce. In the present study, we evaluated natural bacterial and parasitic infections in brown trout (Salmo trutta m. fario) collected from the Černá Opava river (Czech Republic) as a potential source of infections for rainbow trout (Oncorhynchus mykiss) reared in a flow-through farm system fed by the same river. The prevalence of bacterial and protozoan infections in farmed fish was comparable, or higher, than for riverine fish. Despite this, none of the infected farmed fish showed any signs of severe diseases. Substantial differences in metazoan parasite infections were observed between wild and farmed fish regarding monogeneans, adult trematodes, nematodes, the myxozoan Tetracapsuloides bryosalmonae found in riverine fish only, and larval eye-fluke trematodes sporadically found in farmed fish. The...
Diseases of Aquatic Organisms, 2003
In Norway, antibacterial drugs for use in farmed fishes have to be prescribed by a veterinarian. Moreover, a national surveillance programme requires that copies of all prescriptions be sent to the Directorate of Fisheries. The prescriptions give information regarding fish farm and locality, weight and species of fish to be medicated, diagnosis, type and amount of drug prescribed, and date. These prescription data for the 10 yr period 1991 to 2000 have been recorded and systematised. A total of 6322 prescriptions issued for 11 fish species were registered; Atlantic salmon represented 87% of the prescriptions, rainbow trout 4.5%, arctic char 0.3%, turbot 3.8%, halibut 2.1%, Atlantic cod 1.2%, and European eel 0.3%. European sea-bass, wolf-fish, coalfish and wrasse represented a total of 0.4% of the prescriptions. Furunculosis was the most frequently given diagnosis in Atlantic salmon, accounting for 79% of all prescriptions for this species. Furunculosis was more frequent during the summer and early autumn, and in the western parts of Norway. Fish weighing more than 1 kg seemed to be the most susceptible. However, furunculosis has almost disappeared in Norwegian aquaculture since 1993. Vibriosis gave cause for antibiotic treatments in almost all fish species, and was the most common diagnosis in rainbow trout, halibut, turbot, cod and European eel. In Atlantic salmon, fish of small and medium size (up to 1 kg) seemed to be more at risk from vibriosis, and outbreaks were more frequent during summer, and in the western counties. Cold-water vibriosis was the second most frequently treated disease in Atlantic salmon, creating severe problems mainly in larger fish, in the northern parts of the country, and during winter and spring. The seasonal distribution was similar for winter ulcer disease, the only disease which seemed to be of increasing importance in Atlantic salmon. Non-specific diagnoses, such as 'bacterial infection' and 'fry disease', were given in a much higher proportion of prescriptions for marine fish species than in prescriptions for salmonids.
Expert consultation on risk factors for introduction of infectious pathogens into fish farms
Preventive Veterinary Medicine, 2014
An expert consultation was conducted to provide quantitative parameters required to inform risk-based surveillance of aquaculture holdings for selected infectious hazards. The hazards were four fish diseases endemic in some or several European countries: infectious salmon anaemia (ISA), viral haemorrhagic septicaemia (VHS), infectious haematopoietic necrosis (IHN), and koi herpes virus disease (KHD). Experts were asked to provide estimates for the relative importance of 5 risk themes for the hazard to be introduced into and infect susceptible fish at the destination. The 5 risk themes were: (1) live fish and egg movements; (2) exposure via water; (3) on-site processing; (4) short distance mechanical transmission and (5) distance independent mechanical transmission. The experts also provided parameter estimates for hazard transmission pathways within the themes. The expert consultation was undertaken in a 2 step approach: an online survey followed by an expert consultation meeting. The expert opinion indicated that live fish movements and exposure via water were the major relevant risk themes. Experts were recruited from several European countries and thus covered a range of farming systems. Therefore, the outputs from the expert consultation have relevance for the European context. Crown
Ecopathology in aquaculture: risk factors in infectious disease outbreak
Veterinary research, 1995
This paper describes a study of the risk factors associated with disease outbreaks in fish species of fish farms and rivers of north-east Spain. We focused our work on the isolation of fish pathogens (bacteria, virus), the water quality (physicochemical and microbiological quality) and management characteristics. We have observed 2 important viral diseases, infectious pancreatic necrosis and spring viraemia of carp, and 2 important bacterial ones, furunculosis (Aeromonas salmonicida) and bacterial kidney disease (BKD) (Renibacterium salmoninarum). Our preliminary results show that there are some potential risk factors associated with the main diseases of fish, such as fish age, fish species, production system, season and water temperature, but their role depends on the disease.
Risk assessment of the environmental impact of Norwegian Atlantic salmon farming
ICES Journal of Marine Science, 2014
Norwegian aquaculture has grown from its pioneering days in the 1970s to be a major industry. It is primarily based on culturing Atlantic salmon and rainbow trout and has the potential to influence the surrounding environment and wild populations. To evaluate these potential hazards, the Institute of Marine Research initiated a risk assessment of Norwegian salmon farming in 2011. This assessment has been repeated annually since. Here, we describe the background, methods and limitations of the risk assessment for the following hazards: genetic introgression of farmed salmon in wild populations, regulatory effects of salmon lice and viral diseases on wild salmonid populations, local and regional impact of nutrients and organic load. The main findings are as follows: (i) 21 of the 34 wild salmon populations investigated indicated moderate-tohigh risk for genetic introgression from farmed escaped salmon. (ii) of 109 stations investigated along the Norwegian coast for salmon lice infection, 27 indicated moderate-to-high likelihood of mortality for salmon smolts while 67 stations indicated moderate-to-high mortality of wild sea trout. (iii) Viral disease outbreaks (pancreas disease, infectious pancreatic necrosis, heart and skeletal muscle inflammation, and cardiomyopathy syndrome) in Norwegian salmon farming suggest extensive release of viruses in many areas. However, screening of wild salmonids revealed low to very low prevalence of the causal viruses. (iv) From 500 yearly investigations of local organic loading under fish farms, only 2% of them displayed unacceptable conditions in 2013. The risk of eutrophication and organic load beyond the production area of the farm is considered low. Despite several limitations, especially limited monitoring data, this work represents one of the world's first risk assessment of aquaculture. This has provided the Norwegian government with the basis upon which to take decisions for further development of the Norwegian aquaculture industry.
Salmonella in fish feed; occurrence and implications for fish and human health in Norway
Aquaculture, 2007
Globally, Salmonella is one of the most important food borne zoonotic pathogens. Norway has a favourable situation regarding Salmonella, as these bacteria are virtually absent in food producing animals and domestically produced food, including products from fish. Consequently, Norway has a low incidence of domestically acquired salmonellosis in the human population. Some Salmonella serovars can however occasionally be found in animal feed and its ingredients, as well as in the feed production facilities. During the years from 2000 to 2004, the prevalence of Salmonella in samples of feed materials varied from 0.14 to 0.33%. Of environmental samples obtained at Norwegian fish feed production facilities, 3.78% of the examined samples were positive. During the same period, the prevalence of Salmonella in Norwegian ready to use compound fish feed were shown to be 0.3%. The predominant serovars found in fish meal were S. Senftenberg and S. Montevideo. The same serovars were dominating in isolates from the production environment, and could in these cases be considered "house strains". In ready to use compound fish feed, the most common serovars were found to be S. Senftenberg, S. Agona, S. Montevideo and S. Kentucky. Under natural rearing conditions for farmed Atlantic salmon in Norway, and with low concentrations of Salmonella in the feed, the risk of transmission to humans via fish products is minimal. Epidemiological data on salmonellosis from the Norwegian Surveillance System for Communicable Diseases, show that the most common serovars in fish feed ingredients, fish feed and fish feed factories accounts for approximately 2 % of clinical Salmonella isolates from domestically acquired cases in Norway. There is no evidence for transmission of Salmonella from fish feed to humans. However, there is little information on the risk of Salmonella cross-contamination from fish feed, the ingredients and the factories to other parts of society, including wildlife. A probable cross-contamination between fish feed factories and seagulls have been described. The prevalence of antimicrobial resistant Salmonella strains isolated from fish feed, its ingredients and the production environment have so far been very low.
Epizootics of wild fish induced by farm fish
Proceedings of the National Academy of Sciences, 2006
The continuing decline of ocean fisheries and rise of global fish consumption has driven aquaculture growth by 10% annually over the last decade. The association of fish farms with disease emergence in sympatric wild fish stocks remains one of the most controversial and unresolved threats aquaculture poses to coastal ecosystems and fisheries. We report a comprehensive analysis of the spread and impact of farm-origin parasites on the survival of wild fish populations. We mathematically coupled extensive data sets of native parasitic sea lice (Lepeophtheirus salmonis) transmission and pathogenicity on migratory wild juvenile pink (Oncorhynchus gorbuscha) and chum (Oncorhynchus keta) salmon. Farm-origin lice induced 9 -95% mortality in several sympatric wild juvenile pink and chum salmon populations. The epizootics arise through a mechanism that is new to our understanding of emerging infectious diseases: fish farms undermine a functional role of host migration in protecting juvenile hosts from parasites associated with adult hosts. Although the migratory life cycles of Pacific salmon naturally separate adults from juveniles, fish farms provide L. salmonis novel access to juvenile hosts, in this case raising infection rates for at least the first Ϸ2.5 months of the salmon's marine life (Ϸ80 km of the migration route). Spatial segregation between juveniles and adults is common among temperate marine fishes, and as aquaculture continues its rapid growth, this disease mechanism may challenge the sustainability of coastal ecosystems and economies.