Anne Stene

Transmission dynamics of pancreas disease (PD) in a Norwegian fjord: aspects of water transport, contact networks and infection pressure among salmon farms

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.

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.

Maturity classes and spawning behaviour of Greenland halibut (Reinhardtius hippoglossoides)

Abstract The maturation and spawning of Greenland halibut ( Reinhardtius hippoglossoides Walbaum) is described from six trawl surveys in the spawning area along the continental slope between North-Norway and Svalbard from October 1997 to May 1998. Different maturity classes were identified with frequency analyses of logarithmic classes of the Gonadosomatic Index. The main spawning period started in November, peaked in December and ended in late January. Mature females appeared at the spawning area in the early autumn and left during the first months of the year. Males were recorded after this with residual milt, indicating that some spawning may occur several months after the main spawning season. Observations from the fishery indicated spawning concentrations near the coast half a year after the main spawning period. Sex differences in spawning behaviour were discussed and related to the problem of representative sampling.

Seasonal increase in sea temperature triggers pancreas disease outbreaks in Norwegian salmon farms

Pancreas disease (PD) is a viral disease causing negative impacts on economy of salmon farms and fish welfare. Its transmission route is horizontal, and water transport by ocean currents is an important factor for transmission. In this study, the effect of temperature changes on PD dynamics in the field has been analysed for the first time. To identify the potential time of exposure to the virus causing PD, a hydrodynamic current model was used. A cohort of salmon was assumed to be infected the month it was exposed to virus from other infective cohorts by estimated water contact. The number of months from exposure to outbreak defined the incubation period, which was used in this investigation to explore the relationship between temperature changes and PD dynamics. The time of outbreak was identified by peak in mortality based on monthly records from active sites. Survival analysis demonstrated that cohorts exposed to virus at decreasing sea temperature had a significantly longer incubation period than cohorts infected when the sea temperature was increasing. Hydrodynamic models can provide information on the risk of being exposed to pathogens from neighbouring farms. With the knowledge of temperature-dependent outbreak probability, the farmers can emphasize prophylactic management, avoid stressful operations until the sea temperature is decreasing and consider removal of cohorts at risk, if possible.

Estimation of the reproduction number of salmon pancreas disease virus subtype 3 in homogeneously mixed populations of Norwegian farmed Atlantic salmon.

The reproduction number (R) of salmon pancreas disease (PD) was estimated within homogeneously mixing populations (within-cage) of Norwegian farmed Atlantic salmon (Salmo salar L.) based on data collected during PD epidemics from 10 cages at 2 farming sites. Two approaches were used: (a) estimation of an overall reproduction number (R(cmd)) and a time-dependent reproduction number (R(t)) using mortality records during PD epidemics, and (b) estimating the reproduction number during the early stage of infection (R(sd)) based on data from a surveillance program for SPDV subtype 3. The R(cmd) estimates based on the mortality data ranged from 1.02 to 1.45, and the R(sd) estimates ranged from 1.0 to 2.9. Plots of the R(t) estimates covering the whole epidemic period yielded an increasing slope prior to SPDV3 detection. This study presents a framework for the quantitative measurement of a PD epidemic that could be useful for the evaluation of prevention methods. The time-dependent R(t) estimate can provide an early warning of PD outbreaks.

The Phe362Tyr mutation conveying resistance to organophosphates occurs in high frequencies in salmon lice collected from wild salmon and trout

The parasitic salmon louse, and its resistance to chemical delousing agents, represents one of the largest challenges to the salmon aquaculture industry. We genotyped lice sampled from wild salmon and sea trout throughout Norway with the recently identified Phe362Tyr mutation that conveys resistance to organophosphates. These results were compared to data from lice sampled on farmed salmon in the same regions. The resistant (R) allele was observed in salmon lice from wild salmon and sea trout throughout Norway, although its frequency was highest in farming-intense regions. In most regions, the frequency of the R allele was higher in lice collected from wild sea trout than wild Atlantic salmon, and in all regions, the frequency of the R allele was similar in lice collected from wild sea trout and farmed Atlantic salmon. The R allele is only selected for in fish-farms where organophosphates are used for delousing. Therefore, our results suggest extensive exchange of lice between farmed and wild hosts, and indicate that in farming-dense regions in Norway, aquaculture represents a major driver of salmon louse population structure. Finally, these data suggest that the wild hosts within the regions studied will not delay the spread of resistance when organophosphates are used.

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.

Ballast Water Analysis And Heat Treatment Using Waste Heat Recovery Systems On Board Ships.

Ballast water contains a variety of organisms including bacteria, viruses and the adult and larval stages of the many marine and coastal plants and animals. As such, it poses serious ecological, economic and health problems and has serious negative effects on the global environment. This paper presents a new efficient ballast water analysis and heat treatment system using waste heat recovery system on ships. The project demonstrates laboratory methods to verify killing efficiency of microorganisms in sea water exposed to heat treatment over a short period of time. Heating times were varied in a range from 20 seconds to 3 minutes. The microorganisms were measured using a flow cytometry instrument and fluorescence microscopy to detect living and dead organisms in untreated and treated water. Based on the biological analysis, a related heat treatment simulation was carried out to confirm the control method.

Establishment of a non-invasive method for stress evaluation in farmed salmon based on direct fecal corticoid metabolites measurement

Abstract Fish welfare is an important issue for growth of the aquaculture industry. Stress responses represent animals natural reactions to challenging conditions and could be used as a welfare indicator. Cortisol level is relevant to fish welfare condition, and is a readily measured component of the primary stress response system. Generally, cortisol is measured by blood sampling. However, fish blood cortisol level could be instantly influenced by handling‐stress at sampling. Fecal corticoid metabolites (FCM) are a mixture of several different metabolites with a wide range of polarities. Thus, feces could be promising alternative less handling‐sensitive and non‐invasive biological matrices for cortisol evaluation in Atlantic salmon. In this study we developed non‐invasive method for determination of fecal corticoid metabolites in farmed Atlantic salmon (Salmo salar L.) using enzyme‐linked immunosorbent assay (ELISA). It was demonstrated that salmon FCM extracted from salmon feces is insoluble in non‐polar solvents like diethyl ether, but well soluble in polar solvents like methanol. The proper extraction ratio could be one ml 100% methanol for 100 &mgr;L of the liquid part of salmon feces or 100 mg of the solid part. The FCM directly detected in unextracted liquid part of feces correlated well with the FCM extracted from both liquid and solid part of the corresponding samples, without significant difference. Thus, it is feasible to measure FCM directly in the liquid part of salmon feces without any extraction procedure. Then, we applied this assay for FCM analysis in the group of salmon that experienced salmon pancreas disease (PD) and amoebic gill disease (AGD). We demonstrated 1) both plasma cortisol and FCM increased significantly during the outbreak of inflammatory disease (P < 0.01). Plasma cortisol level was elevated from 28 ± 40 ng/ml to 164.4 ± 62.5 ng/ml, FCM from 14.4 ± 13.2 ng/ml to 170.7 ± 89.7 ng/ml 2) Growth and starvation has no significant impact on either cortisol or FCM level. 3) FCM correlated well with plasma cortisol level (P < 0.01). Furthermore, there seems more individual variation in plasma cortisol levels than in FCM levels. These results suggest FCM could be directly analyzed in liquid part of salmon feces without extraction. This directly detected FCM level could represent the total fecal FCM level and plasma cortisol level. This simple and non‐invasive method makes FCM a proper indicator for salmon welfare. HighlightsDirect measurement of fecal corticoid metabolites (FCM) in the liquid part of salmon feces is proposed.Directly detected FCM level could represent the total fecal FCM and plasma cortisol level.The simple and non‐invasive method makes FCM a proper indicator for salmon welfare.