Fish Disease Research Group - FDRG

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Ida Vilinn Tolås

AquaDome: Effect of closed cages on salmon health.
About 20 % of the farmed salmon in Norway is lost as a result of diseases. In addition, surviving salmon, after a disease outbreak, may be downgraded due to quality. The salmon farming industry is also criticized for having a negative impact on the wild salmonids in Norway. A major focus for this criticism is the influence of the salmon louse (Lepeophtheirus salmonis) on wild salmonids. As a response to these problems the industry has developed closed and semi-closed systems for production of salmonids, and one of these systems, the AquaDome, are being tested by EWOS Innovation Dirdal. The test-project will focus on several factors (growth, fish health, behaviour, feed use, mortality, environmental parameters, etc) in a comparative study comparing the AquaDome with production in open nets. The fish were put to sea in March/April 2011 and will be harvested in February 2012. The main aim of the master thesis is to compare of prevalence and density of known salmon pathogens in the open nets and the AquaDome.


Geir Schriwer
Prevalence and densities of selected pathogens in wild populations of Atlantic salmon from five large river systems in western Norway.
Production of Atlantic salmon in Norway has for many years suffered from several diseases resulting in high mortalities. Some of the causative agents are also causing problems for wild salmonids (ex. Lepeophtheirus salmonis), and an additional number have the potential to have a negative influence on wild salmonids (ex: Parvicapsula pseudobranchicola, Paranucleospora theridion, Eubothrium sp., and Flavobacterium psychrophilum). Little has been done to see if any of these may influence on the survival and reproductive success of wild salmon and trout in Norway, but a project to gather information about the distribution, prevalence and intensity of all known salmonid pathogens that may have a negative influence on wild salmonids has been started. Wild salmonids collected in rivers in the counties Rogaland, Hordaland, Sogn og Fjordane and Møre og Romsdal in the period 2009 – 2011 are included in the study. The major focus will be on wild S. salar and some important pathogens that are frequently found in farmed populations in western Norway. A major area of focus will be the Hardangefjord area.


Arnfinn Økland
Development of Paranucleospora theridion in Lepeophtheirus salmonis.
A new microsporidian, Paranucleospora theridion, was detected in Atlantic salmon, trout, rainbowtrout and salmon lice in 2008. This microsporidian has a complex life cycle with the production of four different spores, ie. production of two different spores in salmon and another two in salmon louse. One spore development, resulting in autoinfective spores, occurs in the cell cytoplasm of selected cells in salmon. These spores are spread within the salmon host and may cause an inflammatory response in all tissues (skin, gills, heart, kidney, spleen, pancreas etc). The second spore development occurs in the nucleus of epithelial cells of gills and skin of infected salmon. It is believed that these spores are infective stages for transmission to salmon lice (L. salmonis and Caligus elongatus). P. theridion develops two different spores (micro- and macrospores) in salmon louse. The present study will follow the development of P. theridion in the different stages (chalimi, preadults and adults) of the salmon louse, and give a detailed description of the morphological development in these stages.


Øystein  Staveland
Prevalence and densities of Paranucleospora theridion in wild Atlantic salmon (Salmo salar L.) and sea trout (Salmon trutta L.) in selected areas in Western Norway.
A microsporidian parasite was discovered in farmed Atlantic salmon in 2008. This parasite, Paranucleospora theridion has been shown to be widespread among populations of farmed salmon. It is also was associated with diseases and mortality. The main host for this parasite is salmon lice (Lepeophtheirus salmonis). In this study, real time RT PCR, real time PCR, PCR and sequencing were used to detect and identify the parasite in tissues of two species of wild salmonids, sea trout (Salmo trutta L.) postsmolts and adults with varying sea-age, and adult Atlantic salmon (Salmo salar L.) collected from sea and river localities in Western Norway. In the present study P. theridion infections were found to be common among wild populations of Atlantic salmon and sea trout. The parasite was also detected in salmon lice (Lepeophtheirus salmonis), but at a low prevalence and densities. Sea trout seems to be infected during or shortly after seaward migration and density in gill and kidney tissue increases during summer. In returning Atlantic salmon, the parasite was present with high prevalence and densities in both gill and kidney tissue at the time of collection in late autumn. Densities of P. theridion varied greatly among individuals in the same fish population, reflecting large individual variation in infection levels. It remains to be shown if this parasite influences on the fitness of wild salmonids.

Silje Sveen
Paranucleospora theridion (Microspora) infection dynamics in farmed Atlantic salmon (Salmo salar) put to sea in spring and autumn.
The microsporidian parasite Paranucleospora theridion is a parasite of Atlantic salmon, Salmo salar and a hyperparasite of the salmon louse Lepeophtheirus salmonis. The parasite develops two types of spores in salmon, cytoplasmic spores in phagocytes and intranuclear spores in epidermal cells. The former type of development is assumed to be propagative (autoinfection), while the epidermal spores transfer the parasite to lice. Development in lice is extensive, with the formation of xenoma like hypertrophic cells filled with microsporidian spores. It is shown that salmon is infected in the absence of lice, likely through water borne spores that initiate infections in the gills. During summer-autumn the parasite propagates in the kidney, as evidenced by peaking normalized expression of P. theridion rDNA. Lice become infected during autumn, and develop extensive infections during winter. Lice mortality during winter-spring is likely responsible for a reservoir of spores in the water. Salmon transferred to sea in November (low temperature) did not show involvement of the kidney in parasite propagation and lice on such fish did not become infected. Apparently, low temperatures inhibit normal P. theridion development in salmon.


Asbjørn Durkorn Løland
Phenotypic and genotypic characterization of Flavobacterium spp. from salmonids
The last few years have seen a dramatic increase of disease outbreaks in Norwegian salmon and rainbow trout farms caused by Flavobacterium psychrophilum. This pathogen has previously not been a problem in Norwegian fish farming, but a recent increase in outbreaks of disease caused by F. psychrophilum causes reason for concern. This study set out to investigate the diversity of Norwegian F. psychrophilum strains with the purpose of comparing them to previously characterized strains with global diversity. A partly polyphasic approach was applied to characterize the different Flavobacterium isolates. This approach included the use of several phenotypic methods such as API ZYM, growth media and growth temperature among others. It also included genotypic characterization by the use of phylogenetic analyzes based on the 16S rRNA gene and seven housekeeping genes including the atpA-, dnaK-, fumC-, gyrB-, murG-, trpB- and the tuf-gene. The results from the phenotypic characterization of the Flavobacterium sp. isolates were in accordance to previously described flavobacteria and the genotypic characterization confirmed the isolates within the Flavobacterium genus. 16S rRNA gene analysis revealed relatively high homology between different Flavobacterium species, which resulted in low resolution of the phylogenetic trees. Percentage sequence identity of housekeeping genes among the Flavobacterium sp. isolates were, however, low and combined with differences in the phenotypic profiles these results were indicative of the discovery of new species within the Flavobacterium genus. Comparing the housekeeping genes from F. psychrophilum as concatenated sequences to previously characterized strains with world wide distribution revealed identical strains located in Norway, France, Denmark and Switzerland. This indicates vertical transmission through international trade of fish eggs.

Sindre Strandos
Studie av variabel del i ikkje-strukturelt protein 3 hjå Salmonid alfavirus.
Pancreas disease (PD) og Sleeping disease (SD) er fiskesjukdomar som råkar atlantisk laks (Salmo salar, L) og regnbogeaure (Oncorhynchys mykiss, Walbaum) innan europeisk oppdrettsnæring. Desse fiskesjukdommane blir årsaka av Salmonid alfavirus (SAV), som høyrer til familien Togaviridae. SAV er delt inn i seks ulike subtypar (SAV1-6), der berre genomet til SAV1-3 er fullstendig sekvensert. Det ikkje-strukturelle proteinet nsP3 har med sin variable C-terminal vist seg å vere ein del av replikasjonskomplekset til Alfavirus, og hjå SAV er det variasjonane i nsP3 som utgjer dei største skilnadane i gensekvens mellom dei ulike subtypane av viruset. Sjølv om det for Alfavirus er føreslått at faktorar som er viktige for
syntese av RNA, virulens og vektortilpassing er lokalisert i den variable delen av nsP3, er det elles lite ein veit om kva funksjonelle skilnadar desse variasjonane utgjer for dei tre fullstendig sekvenserte subtypane av SAV. I dette studiet har ein bytta ut den variable delen av nsP3 hjå SAV3 med tilsvarande del frå SAV1 og SAV2. Dette blei gjort for å undersøkje kor mykje variasjonane i nsP3 har å seie for replikasjonen av SAV. Ved å nytte seg av SAV3-
baserte replikon, fekk ein konstatert at SAV3 framleis var i stand til å replikere sitt genom og uttrykke subgenomisk mRNA etter at variabel del i nsP3 var bytta ut med tilsvarande variabel
del frå SAV1 og SAV2. I tillegg fekk ein vist at SAV3 er i stand til å fullføre ein fullstendig replikasjonssyklus når variabel del frå SAV1 nyttast i SAV3 genomet, noko som resulterte i at ein fekk danna rekombinante infektive viruspartiklar frå fullengdeklon.