Molecular tracing confirms that infection with infectious pancreatic necrosis virus follows the smolt from hatchery to grow‐out farm

Infectious pancreatic necrosis (IPN) is an important restraint to production of salmonids in aquaculture globally. In order to implement efficacious mitigation strategies for control of this disease, it is important to understand infection routes under current production systems. IPN virus has been shown to be transmitted vertically in Rainbow trout, from broodstock to fingerlings in hatcheries, and there is circumstantial evidence suggesting that vertical transmission can also occur in Atlantic salmon, in addition to horizontal transmission between grow‐out fish in farms. In this study, we show that the smolt carries infection with IPN from hatchery to the marine farm. We do this by comparing sequences from fish groups taken both in hatcheries and on corresponding marine grow‐out farms. We use statistical analysis to prove that sequences obtained from the same fish group in both hatchery and marine farm are more similar than sequences obtained from random fish groups on hatcheries and marine farms.     

Landscape heterogeneity and the effect of environmental conditions on prairie wetlands

Populations can vary considerably in their response to environmental fluctuations, and understanding the mechanisms behind this variation is vital for predicting effects of environmental variation and change on population dynamics. Such variation can be caused by spatial differences in how environmental conditions influence key parameters for the species, such as availability of food or breeding grounds. Knowing how these differences are distributed in the landscape allows us to identify areas that we can expect the highest impact of environmental change, and where predictions on population dynamical effects will be most precise. We evaluated how wetland dynamics in the North-American prairies (pond counts; a key parameter for several waterfowl populations) were related to spatial and temporal variation in the environment, as measured by weather variables, primary productivity and phenology derived from annual normalized difference vegetation index (NDVI) curves, and agricultural composition of the landscape. Spatial and temporal variation in pond counts were closely related to these environmental variables. However, correlation strength and predictive ability of these environmental variables on wetland dynamics varied considerably across the study area. This variation was related to landscape characteristics and to the spatial scaling of the wetland dynamics, such that areas with late onset of spring, low spring temperature, high primary productivity, and high proportion of cropland had more predictable and spatially-homogenous dynamics. The success of predicting environmental influences on wetlands from NDVI measures derived from satellite images indicates they will be useful tools for assessing effects of changing landscape and climatic conditions on wetland ecosystems and their wildlife populations.     

Brucella pinnipedialis hooded seal (Cystophora cristata) strain in the mouse model with concurrent exposure to PCB 153

Brucellosis, a worldwide zoonosis, is linked to reproductive problems in primary hosts. A high proportion of Brucella-positive hooded seals (Cystophora cristata) have been detected in the declined Northeast Atlantic stock. High concentrations of polychlorinated biphenyls (PCBs) have also been discovered in top predators in the Arctic, including the hooded seal, PCB 153 being most abundant. The aim of this study was to assess the pathogenicity of Brucella pinnipedialis hooded seal strain in the mouse model and to evaluate the outcome of Brucella spp. infection after exposure of mice to PCB 153. BALB/c mice were infected with B. pinnipedialis hooded seal strain or Brucella suis 1330, and half from each group was exposed to PCB 153 through the diet. B. pinnipedialis showed a reduced pathogenicity in the mouse model as compared to B. suis 1330. Exposure to PCB 153 affected neither the immunological parameters, nor the outcome of the infection. Altogether this indicates that it is unlikely that B. pinnipedialis contribute to the decline of hooded seals in the Northeast Atlantic.     

Larval group differentiation in Atlantic cod (Gadus morhua) inside and outside the Gullmar Fjord

The spatial and temporal occurrence of pelagic fish stages and their biological variability may affect their dispersal and survival, and ultimately fish recruitment. We collected Atlantic cod larvae at one station inside and at one station outside the Gullmar Fjord, eastern Skagerrak, in order to investigate small-scale larval group differentiation. Rectangular midwater trawl hauls were taken every 6 h (during 24 h) from three separate depth intervals between the surface and 70 m depth. About 80% and 20% of all larvae occurred above the halocline at the Fjord station and the Coastal station, respectively. Hatching (at both stations) occurred from the 3rd week in February to the 1st week in May, indicating that cod larvae were present for at least 5 months (from late February to early August). The length and hatch date frequency distributions of larvae from the surface layer were unimodal inside the fjord but bimodal outside the fjord. Analyses of seven microsatellite DNA loci indicated that larvae collected inside the fjord (where local spawning occurs) were genetically distinct from larvae sampled on the outside (F_ST = 0.0026). The two age cohorts outside the fjord were not, however, genetically different, nor were larvae collected at different depths. We conclude that small-scale variability of vertical concentration and larval life history variability should have consequences for interpreting models of larval dispersal and survival, and subpopulation structure analyses.     

Liquid fat,a potential abiotic vector for horizontal transmission of salmonid alphavirus?

Viral diseases represent serious challenge in marine farming of Atlantic salmon (Salmo salar L). Pancreas disease (PD) caused by a salmonid alphavirus (SAV) is by far the most serious in northern Europe. To control PD, it is necessary to identify virus transmission routes. One aspect to consider is whether the virus is transported as free particles or associated with potential vectors. Farmed salmonids have high lipid content in their tissue which may be released into the environment from decomposing dead fish. At the seawater surface, the effects of wind and ocean currents are most prominent. The aim of this study was primarily to identify whether the lipid fraction leaking from dead infected salmon contains SAV. Adipose tissue from dead SAV‐infected fish from three farming sites was submerged in beakers with sea water in the laboratory and stored at different temperature and time conditions. SAV was identified by real‐time RT‐PCR in the lipid fractions accumulating at the water surface in the beakers. SAV‐RNA was also present in the sea water. Lipid fractions were transferred to cell culture, and viable SAV was identified. Due to its hydrophobic nature, fat with infective pathogenic virus at the surface may contribute to long‐distance transmission of SAV.     

Goshawk breeding densities in relation to mature forest in southeastern Norway

Forest harvesting practices have been assumed to be the main reason for the decrease in Goshawk Accipiter gentilis populations in Fennoscandia during the late 1900s, by reducing prey density, especially grouse and Red Squirrel (Sciurus vulgaris), and preferred hunting habitats (mature forest). In Norway, the highest breeding densities are now found in areas with a high proportion of farmland and urban areas where corvids and pigeons are important prey. To assess the importance of mature forest for Goshawk populations in southeastern Norway, we compared breeding densities from 20 municipalities with different percentages of farmland and mature forest. In multiple regression models, regional breeding densities were positively related to both the percentage of mature forest, and the percentage of farmland and urban areas. We conclude that the recommendation of establishing buffer zones around nest sites will not be sufficient to maintain Goshawk populations if the proportion of mature forest is reduced at a landscape level.     

Lack of evidence for vertical transmission of SAV 3 using gametes of Atlantic salmon, Salmo salar L., exposed by natural and experimental routes

Pancreas disease (PD) is an important cause of losses in farmed salmonids in Norway, the United Kingdom and Ireland. As the spread of salmonid alphavirus (SAV), the causal agent, to naïve populations is of major concern to the farming industry, it is important to uncover the transmission routes of the virus. This study was conducted to investigate the potential for vertical transmission of SAV subtype 3. Progeny of broodstock with signs of late‐stage PD and persistent RT‐PCR signals for SAV were followed from fertilization to smoltification in an experimental facility. Fertilized ova were either not disinfected or taken through one of three different disinfection regimes. Also, ova and milt from uninfected broodfish from a different population were exposed to a cell‐cultured strain of SAV 3 immediately before fertilization to simulate a viraemic phase in parent fish. A group of uninfected controls were also included in the study. Fertilized ova from bath exposed and negative control groups were double disinfected. Following fertilization, experimental fish went through a normal freshwater phase. However, fry were stressed at first feeding to enhance replication of possibly latent virus. Smoltification was induced by an artificial light regime, and experimental fish were followed to the late smoltification phase. Selected samples were investigated by real‐time RT‐PCR for SAV, by histology for evidence of PD and by serology for neutralising antibodies against SAV. All analysed samples of progeny were negative. This result shows that SAV 3 is not readily transmitted vertically from parents to offspring. Additional negative PCR results from salmon sampled in commercial hatcheries support these findings. Also, recent studies have shown that risk factors for the horizontal transmission route explain the vast majority of PD outbreaks in Norway. It is concluded that if it happens at all, vertical transmission is of minor importance in the spread of SAV 3.     

Induction of polyploidy in salmonids by cytochalasin B

The purpose of this study was to investigate the possibility of producing tetraploid fishes. Eggs of salmon (Salmo Salar) and rainbow trout (Salmo gairdneri) were treated with concentrations of cytochalasin B ranging from 1 μg/ml to 100 μg/ml for varying periods of time. All treated groups had higher death rates than untreated controls. If the treatment was started immediately after fertilization and before the eggs had swollen all eggs died. The highest frequency of mosaic embryos and polyploid cells was obtained when the treatment started 35–70 h° (hour-degrees) after fertilization and lasted until about the 4-cell stage of development. A dose of 10 μg/ml of cytochalasin B gave the most satisfactory results. This concentration was used for further work. Two batches of 6000 salmon eggs and several groups of rainbow trout eggs were treated and hatched. The hatchability was generally low while the control group had a normal hatchability. If some of the treated fish are eventually found to be tetraploids and fertile, they will be used to produce triploid offspring by crossing with normal diploid fish.     

When counting cattle is not enough: multiple perspectives in agricultural and veterinary research

A traditional approach in agricultural and veterinary research is focussing on the biological perspective where large cattle-databases are used to analyse the dairy herd. This approach has yielded valuable insights. However, recent research indicates that this knowledge-base can be further increased by examining agricultural and veterinary challenges from other perspectives. In this paper we suggest three perspectives that may supplement the biological perspective in agricultural and veterinary research; the economic-, the managerial-, and the social perspective. We review recent studies applying or combining these perspectives and discuss how multiple perspectives may improve our understanding and ability to handle cattle-health challenges.