Proliferative gill inflammation (PGI) is an important cause of loss in seawater-farmed Atlantic salmon in Norway. Several microbes have been associated with PGI, including the commonly but not exclusively observed inclusions (epitheliocysts) within the gill lamellae related to infection with 'Candidatus Piscichlamydia salmonis'. Atlantic salmon transferred in the spring of 2004 to 12 seawater farms situated in mid-and southwest Norway were sampled throughout that year. Outbreaks of PGI, as evaluated by clinical examination, histology, and mortality data, were diagnosed in 6 of 7 farms in southwest Norway but not in the 5 farms studied in mid-Norway. Generally, mortality started 3 to 5 mo after seawater transfer and outbreaks lasted at least 1 to 3 mo. 'Ca. P. salmonis' was detected by real-time PCR only in fish from PGI-affected farms and our results indicate an association between 'Ca. P. salmonis' load and PGI severity. Likewise, although widely distributed in all 12 farms studied, epitheliocyst prevalence and number per fish as observed by histology appears associated with PGI prevalence and severity. However, the occurrence of epitheliocysts showed no association with molecular detection of 'Ca. P. salmonis', suggesting that at least 1 other organism is responsible for many of the observed inclusions. A microsporidian, Desmozoon lepeophtherii, was identified at high prevalence regardless of fish and farm PGI status, but at higher loads in fish with PGI. Our results support a multifactorial etiology for PGI in which 'Ca. P. salmonis', an unidentified epitheliocyst agent, and the microsporidian are contributing causes. No evidence for the involvement of Atlantic salmon paramyxovirus in PGI development was identified in the present study. High water temperatures and ectoparasites probably exacerbated mortality. KEY WORDS: Proliferative gill inflammation · Epitheliocysts · 'Candidatus Piscichlamydia salmonis' · Desmozoon lepeophtherii · 'Candidatus Clavochlamydia salmonicola' · Atlantic salmon paramyxovirusResale or republication not permitted without written consent of the publisher Dis Aquat Org 91: 201-211, 2010 to months (Kvellestad et al. 2004, Skjelstad et al. 2007. Mortality varies and losses of 15 to 20% or higher have been reported (Flesjå et al. 2004, Kvellestad et al. 2004. Estimation of economic losses is difficult, but one of the largest farming companies in Norway considered PGI to be the disease responsible for most losses in terms of both numbers of fish and biomass in 2007(Skjelstad et al. 2007). Gill disorders were also the most important cause of losses in Ireland in 2005(Rodger 2007. Previous studies have indicated a multifactorial etiology behind PGI, following identification of various microorganisms occurring alone or in combination with others, including Atlantic salmon paramyxovirus (ASPV) (Kvellestad et al. 2003(Kvellestad et al. , 2005, salmon gill poxvirus , various ectoparasites (Kvellestad et al. 2005), as well as lamellar bacterial inclusions (epitheliocystis) (Nylund ...

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Aims: To investigate the relationships between water temperature, bacterial growth, virulence and antigen expression in Vibrio salmonicida, the causal agent of cold water vibriosis in Atlantic salmon (Salmo salar L.). Methods and Results:The significance of sea temperature was investigated using historical clinical and oceanographic data. An upper threshold for disease of approx. 10°C was established. The effects of culture temperature and media type on bacterial growth were studied on solid and in liquid media. The highest rates of cell division were identified at 15°C on solid media and 10°C in liquid media. Outer membrane protein (OMP) expression and serological response in Atlantic salmon were studied using sodium dodecyl sulphatepolyacrylamide gel electrophoresis, Western blotting and enzyme-linked immunosorbent assay. A novel 76-kDa OMP produced in unshaken cultures at 10°C was not found to stimulate a specific humoral response. Conclusions: Diagnostic agar plate-based incubation of suspected V. salmonicida should be carried out at 15°C. High yield broth cultures for vaccine production should be incubated at 10°C or lower. Significance and Impact of the Study: This study is, to the best of our knowledge, the first to identify different optimal temperatures in a bacterial species cultured on physically different types of media. The evidence presented suggests that V. salmonicida and possibly other bacteria destined for vaccine use in poikilothermic organisms should be cultured at temperatures consistent with that at which disease occurs.

MIC testing of Vibrio anguillarum isolates recovered from diseased farmed Atlantic cod revealed oxolinic acid MICs of ≤0.001, 0.06, and 16 μg ml−1. Single gyrA Ser-Ile substitutions were identified at position 83 of the intermediate and resistant strains, while a parC Ser-Leu substitution at position 85 was found only in the resistant strain.