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Pancreas disease ( PD) in marine salmon farming is caused by salmon pancreas disease virus ( SPDV). Virus survival, infection pressure and contact networks among farms influence the potential of PD to spread. The present study aims to explore contact networks and infection pressure and their ability to explain transmission dynamics of PD in a Norwegian fjord. In this study, we included all records of PD by subtype 3 ( SPDV3) in the study population from the first reported in August 2006 to the last reported in November 2009. Using logistic regression analyses, we found that contact network by water transport explained better transmission of PD than contact networks defined by ownership or close distance to infected farms. Hydrodynamic modelling can be a valuable tool to forecast the spread of PD and thereby take actions to reduce the transmission. Knowing the risk of getting infected, it is important to avoid water transport from infected farms when new cohorts are transferred to sea water, and to have conscious control regarding management operations between farms. [ABSTRACT FROM AUTHOR]

This is the first comprehensive study on the occurrence and distribution of piscine reovirus ( PRV) in Atlantic salmon, Salmo salar L., caught in Norwegian rivers. PRV is a newly discovered reovirus associated with heart and skeletal muscle inflammation ( HSMI), a serious and commercially important disease affecting farmed Atlantic salmon in Norway. A cross-sectional survey based on real-time RT- PCR screening of head kidney samples from wild, cultivated and escaped farmed Atlantic salmon caught from 2007 to 2009 in Norwegian rivers has been conducted. In addition, anadromous trout (sea-trout), Salmo trutta L., caught from 2007 to 2010, and anadromous Arctic char, Salvelinus alpinus (L.), caught from 2007 to 2009, were tested. PRV was detected in Atlantic salmon from all counties included in the study and in 31 of 36 examined rivers. PRV was also detected in sea-trout but not in anadromous Arctic char. In this study, the mean proportion of PRV positives was 13.4% in wild Atlantic salmon, 24.0% in salmon released for stock enhancement purposes and 55.2% in escaped farmed salmon. Histopathological examination of hearts from 21 PRV-positive wild and one cultivated salmon (Ct values ranging from 17.0 to 39.8) revealed no HSMI-related lesions. Thus, it seems that PRV is widespread in Atlantic salmon returning to Norwegian rivers, and that the virus can be present in high titres without causing lesions traditionally associated with HSMI. [ABSTRACT FROM AUTHOR]

The aim of this study was to model sea lice levels and the effect on reproduction by a stochastic simulation model and to evaluate the uncertainty of lice estimates based upon counts. Two empirical data sets were examined to parameterize the models. An overall fit of the data to the Poisson distribution was found and thus was used as the base of the stochastic models. In the model, salmon lice reproduction is not linear with the number of adult females and at low lice loads a smaller proportion of the adult female lice will reproduce. Depending on the variance structure, it was estimated that between 40% and 60% of the adult female lice will reproduce at an abundance of 0.5 adult females per fish. Lice counts, especially when examining few fish at low lice loads, are uncertain and at a true abundance of 0.1 one may count between 0 and 5 lice when examining 10 fish. Understanding the dynamics of sea lice reproduction is a key factor in the development of sustainable control strategies. [ABSTRACT FROM AUTHOR]

Infectivity of internal organs and cells of Atlantic salmon, Salmo salar L., was studied at various times after infection with the aetiological agent of infectious salmon anaemia (ISA). Experimentally infected salmon smolts developed anaemia just prior to the onset of ISA-mortality. ISA-infectivity of preparations made from liver, kidney. spleen, plasma red blood cells (RBC) and head kidney leucocytes was determined by inoculating Atlantic salmon part with the respective preparations. ISA-mortality was observed after inoculation of salmon pan with preparations of kidney and liver and to a minor degree, with spleen and a fraction of head kidney leucocytes (WBC1) collected 7 days post-infection. At 11 days post-infection, the infectivity of these preparations increased and ISA-infectivity was also observed with a second fraction of head kidney leucocytes (WBC2), red blood cells (RBC) and blood plasma. At this time, the ISA-infectivity of kidney was not significantly higher (P> 005) than that of liver but was significantly higher than all other preparations as judged by Cox-regression analysis. At days 14 and 18 post-infection, the infectivity of kidney was significantly higher (P < 0.05) than that of liver, but not at 21 and 25 days post-infection. Generally, the ISA-infectivity of kidney was higher than spleen, head kidney leucocytes (WBC1 and WBC2), RBC and plasma, although the difference was not significant at all time points. For example, at day 25 post-infection, the infectivity of kidney was only significantly higher than that of spleen and plasma. On a per gram basis, head kidney leucocytes proved to contain higher amounts of infectious matter than RBC. ISA-infective leucocytes present in the kidney tissue may have contributed to a major part of the infectivity recognized in the kidney preparations. Thus, head kidney leucocytes and other kidney leucocytes also may be considered to be among the most important target cells of the aetiological agent of ISA. [ABSTRACT FROM AUTHOR]