salmon

Atlantic salmon postsmolts were exposed to either chronic hypoxic (Hy) or normal oxygen (No) conditions in seawater tanks for 58 days, mimicking conditions typical of sea cages for farmed salmon at some periods of the year. By day 29 head kidney macrophages were isolated and subjected to in vitro poly I:C stimulation to simulate viral infection, and samples were collected over 48 hours. By day 58 fish were subjected to in vivo stimulation using poly I:C or a Vibrio water based vaccine to simulate viral or bacterial infection, respectively. The fish were monitored for stress responses and expression of several pro-inflammatory genes in head kidney and intestinal tissue up to five days post injection. Stress load was monitored by plasma cortisol estimation at days 29 and 58, and on days 1, 2, 3 and 5 post injection in the in vivo trial. Hy exposure resulted in elevated plasma cortisol levels on day 29 compared to No, while on day 58 cortisol levels were higher in the control group. Additionally, both poly I:C and the Vibrio vaccine gave significantly increased cortisol levels one day post injection compared to PBS treated controls, irrespective of previous oxygen exposure. In vitro stimulation of macrophages with poly I:C revealed higher IFNα mRNA levels at 6, 12 and 24h and for Mx at 12 and 24h post stimulation, for both No and Hy individuals. Moreover, IFNα levels where higher in No than in Hy individuals at all time points, and a similar difference were seen in Mx at 48hrs. In vivo stimulation with poly I:C elicited strong elevation of the IL-1β, IFNγ, Mx and IP10 mRNA transcripts in head kidney, while TNFα1 and IFNα were found unaffected. The Vibrio vaccine elicited a strong up regulation of IL-1β, IFNγ and IP10 mRNA, whereas Mx, TNFα1 and IFNα appeared unchanged. Significant differences in expression between different oxygen exposure groups were found for all genes and both stimuli. The overall trend suggests that long term hypoxia either reduces or delays the expression of these genes in head kidney. Expression of IFNγ and Mx in intestinal tissues also showed a strong up regulation of the genes following poly I:C stimulation, and also here the overall trend suggests that chronic hypoxia results in a lower or delayed expression of the measured genes. In summary, our results indicate that chronic hypoxia modulate the expression of important immune related genes putatively altering the immune response. As the effect is present in isolated macrophages as well as head kidney and intestinal tissue the modulation appears to be affecting local as well as systemic responses.

Bjørn Olav Kvamme, Koestan Gadan, Frode Finne-Fridell, Lars Niklasson, Henrik Sundh, Kristina Sundell, Geir Lasse Taranger, Øystein Evensen

Aquaculture faces many threats, including diseases, of which some are notifiable under current UK regulation, e.g. infectious salmon anaemia (ISA) and infectious haematopoietic necrosis (IHN). Abnormal mortality is one possible indicator of the presence of infectious disease on a site that may be used, by the regulator, as a surveillance alert that allows them to identify possible notifiable diseases and to activate measures of control to reduce the risk of spreading those diseases. Therefore, mortality records at the farm level may be a useful indicator for regulatory surveillance purposes in order to identify potential disease outbreaks. In the UK, regulators and producers have discussed abnormal rates of mortality that may be considered as a trigger to notify the official regulator. In our study, the receiver operating characteristic (ROC) approach was used on mortality data from production cycles of a site production database of marine Atlantic salmon belonging to a single company. The usefulness of these data in helping detection of infectious diseases was determined using measures of sensitivity and specificity. For fish under 750g, the abnormal rates of mortality did not provide a strong indication of the presence of disease. The area under the curve (0≤AUC≤1) values were generally low with the exception of cardiomyopathy syndrome (CMS) that showed AUC=0.77 for weekly mortality and AUC=0.73 for five-week rolling mortality. However, abnormal levels of mortality for fish with weight over 750g provided a strong indication of the presence of disease with the exception of both suspected and confirmed IPN. The probabilities of triggering official notification were low since mortality events over the percentages proposed happened infrequently. The most efficient trigger will be for weekly mortality (1%) for fish with weight over 750g since abnormal mortalities in such large fish are more likely to be associated with the presence of disease.

Silvia Soares, Alexander G. Murray, Mags Crumlish, James F. Turnbull, Darren M. Green

There is a growing concern about the welfare of farmed fish. Current breeding programs typically focus on profitability through emphasizing fast growth of the fish. This research, however, finds that a representative sample of Norwegian households are willing to pay an increased tax for farmed Atlantic salmon that is selected for traits related to fish welfare. In an internet survey, a random and representative sample of Norwegian households were asked to choose among breeding programs for farmed Atlantic salmon that differed with regards to costs and the following four traits related to fish welfare; frequency of deformities (Deform), frequencies of injuries (Injur), resistance to salmon lice (Lepeophtheirus salmonis) (Lice) and resistance to diseases (Health). The survey participants were given six different choice sets, and in each they chose one of three alternative salmon breeding programs. Two of the alternative breeding programs would give improvements in at least one of the trait attributes and would result in an earmarked tax per household per year. The third alternative was the status quo option, i.e. a zero earmarked tax with focus only on growth enhancing traits and profitability in breeding programs. Based on the estimation results of random parameter logit models mean willingness to pay (WTP) was estimated for all households and for the subsample of households purchasing farmed salmon. The average WTP was higher for the subsample that purchases farmed salmon compared to the full sample. For households that purchase farmed salmon, the average WTP in terms of an earmarked tax for all attributes were significant and highest for Lice (1034 NOK/yr), followed by Health (749 NOK/yr). The WTP for Deform (282 NOK/yr) and Injur (256 NOK) were nearly the same. For the full sample of household, the average WTP was significantly different from zero at the 5% level only for Health (613.1 NOK/yr) and Lice (951.2 NOK/yr). This study provides evidence that there is a high WTP among all Norwegian households to improve the welfare of farmed Atlantic salmon through increased resistance to diseases and salmon lice, which may imply less use of medicines and chemicals in the production process. Only households that purchase farmed salmon are willing to pay an earmarked tax to reduce deformities and injuries.
K.M. Grimsrud, H.M. Nielsen, S. Navrud, I. Olesen

Epidemiological studies of pancreas disease (PD) in Scottish farmed Atlantic salmon (Salmo salar L.) were conducted by analysing a marine Atlantic salmon farming company's production data on over 60million fish between 1998 and 2009. Presumptive PD diagnoses were made by farm managers with advice from fish health professionals. Mortality ascribed to PD was negligible before 2003 but rose to a peak in 2006 and 2007, accounting for 94% and 86% of disease losses in 2006 and 2007 respectively, followed by a decline in 2008 and 2009. PD mortalities primarily were reported in larger fish (2–5kg) and accounted for the largest loss in biomass due to any infectious disease including infectious pancreatic necrosis (IPN). The mean monthly numbers of fish lost to PD were higher in July through September. The distribution of mortality between PD infected production cycles was highly skewed with one production cycle accounting for 26% of the total reported mortality. The results showed no evidence that PD in a production cycle was related to a subsequent PD outbreak (with an odds ratio of 0.93 relative to farms that had not experienced PD however this OR has large confidence intervals). The analysis of the industry production data has provided information on the prevalence, intensity and spread of PD in Scotland at a level of detail and, crucially, over a relatively long period that would be impossible to obtain from official statistics on this non-notifiable disease.
R. Kilburn, A.G. Murray, M. Hall, D.W. Bruno, D. Cockerill, R.S. Raynard

During the course of a multi-site clinical field trial comparing the field effectiveness of Atlantic salmon (Salmo salar L.) vaccines, an opportunity arose to examine the potential effects of repeated fish handling on the controlled trial outcome. Fish-level data obtained by seining, dip-netting and anesthetizing each of the fish among eight study populations comprising approximately 6000 individually tagged fish per group, provided detailed follow-up for the planned clinical trial. However, the stressful conditions generated during the sampling process resulted in variable post-handling mortality which also provided the unplanned opportunity to evaluate the effect of field procedures on survival. A multilevel mixed effects logistic regression model was used to analyze factors related to mortality occurring in the two-week period following scheduled fish handling events. Data on individual fish level characteristics such as weight, length, sex, physical deformities, lesions, vaccine group allocation, days since vaccination, days since transfer to seawater, and elapsed time spent in the seine were recorded for every fish at each sampling event. In total, the dataset included information on 58,923 fish from 13 sampling events, and contained a total of 648 mortalities. Vaccine group membership was not found to have a significant impact on mortality (p=0.45). Fish with opercular and spinal deformities were found to have significantly higher odds of mortality compared to fish without deformities (odds ratio (OR)=1.77, p=0.001 and OR=2.88, p<0.001, respectively). Gender was found to be a significant predictor of mortality, with females having significantly greater odds of mortality compared to males in the two-week post-handling period (OR=1.28, p=0.002). The time of sampling relative to smolt transfer (i.e. first-year vs. second-year of seawater production) was found to significantly predict mortality (OR=47.6 for second year vs. first year, p<0.001). Significant interactions with the timing of the sampling event (first-year vs. second-year) were found for both weight and seine residence times (p<0.001 for both). A 100g increase in weight at the time of sampling, had significantly less impact on the mortality in sampling events during the second-year of saltwater production than those in the first-year (OR=0.641 vs. 0.937). The impact of each additional hour in seine residence time was greater in first-year sampling events compared to second-year sampling events (OR=2.38 vs. 1.28 respectively; both with p<0.001). While the effect of vaccine group allocation on survival was not found to be influenced by the intensive sampling regime outlined in the controlled field trial protocol, fish characteristics such as spinal deformity, opercular deformity and sex were found to have a significant impact on mortality. The distribution of these population characteristics is difficult to control in field trials in a commercial setting, emphasizing the need for random allocation to evenly distribute these potential confounders to treatment groups. Furthermore, recording and incorporating such variables in the statistical analysis of field trials with repeated handling events provide an assessment of their outcomes.
Timothy Burnley, Henrik Stryhn, K. Larry Hammell

Sea lice (Lepeophtheirus salmonis) are the most economically important ectoparasites affecting Atlantic salmon (Salmo salar) culture worldwide. In recent years the efficacy of historically successful treatments has been on the decline. As such, a new management strategy for controlling lice infections is a high priority for the salmon farming industry. In this study, we tested the ability of three orally administered immunostimulants to decrease the number of lice successfully infecting Atlantic salmon post-smolts. It was found that the β-glucan (ProVale) fed group actually maintained more sea lice than did the control group (24% increase). However, both the CpG ODN (31–46%) and AllBrew NuPro (11–31%) fed groups showed decreased infection levels when compared to the control group. Histopathological and differential gene expression analyses indicate that localized and systemic inflammatory mechanisms may be transiently altered by these immunostimulatory feeds and may result in increased host resistance to sea lice.
J.M. Covello, S.E. Friend, S.L. Purcell, J.F. Burka, R.J.F. Markham, A.W. Donkin, D.B. Groman, M.D. Fast

The large amount of fish feed involved in salmon aquaculture results in high nutrient loading to the surrounding environment. The near-field effects of this loading are well documented but the full zone of influence, or far-field effect, remains poorly understood. We investigated the potential of the carotenoid canthaxanthin, a common additive in farmed Atlantic salmon diets, as a biochemical tracer to identify this zone of influence in two benthic invertebrate species that are locally abundant around salmon farms: the blue mussel Mytilus edulis (or Mytilus trossulus), a suspension feeder, and the green sea urchin Strongylocentrotus droebachiensis, an omnivorous grazer. To measure persistence of canthaxanthin in the digestive gland of mussels or the gonad of sea urchins, both species were individually fed three levels of salmon feed (6, 13, 26mgd⁻¹ for mussels; 70, 150, 300mgd⁻¹ for sea urchins) for 13d to measure pigment uptake rates, followed by a non-pigmented diet for 7d to measure pigment loss rates. Mussels exhibited a relatively rapid uptake of canthaxanthin (1 to 3d), which subsequently declined to zero within 3d following cessation of the pigmented diets. The sea urchins exhibited slower initial uptake (4 to 10d) and the pigment signal lasted up to 46d, suggesting retention of canthaxanthin. To examine the scale of dispersion of feed-derived particulate material in nature, canthaxanthin uptake by sea urchins was measured at fixed intervals along a transect extending 1km from a salmon cage in Passamaquoddy Bay, New Brunswick, Canada. Pigment concentration in the gonad dropped from ~5 to 0.5μgg⁻¹ within the first 100m from the cage and remained at this low level along the remainder of the transect, likely reflecting low background levels of salmon farm-derived particles within the bay. Our study demonstrates the potential of canthaxanthin as an organic tracer for salmon aquaculture, and the use of blue mussel digestive gland for short-term detection and sea urchin gonad for long-term detection, in accordance with the rapid ingestion and nutrient storage functions of the respective tissues.
Carissa M. Graydon, Shawn M.C. Robinson, Robert E Scheibling, J. Andrew Cooper

We present here the first evidence of the presence of iron uptake mechanisms in Streptococcus phocae, a beta-hemolytic bacterium frequently involved in disease outbreaks in seals causing pneumonia or respiratory infection as well as warm water streptococcosis in Atlantic salmon (Salmo salar). Fifteen Atlantic salmon isolates and type strain were able to grow in the presence of the chelating agent 2,2-dypiridyl and produced siderophores using the universal Chrome Azurol S assay in solid and liquid media. Based on the biochemical homogeneity of the bacterium and the results of the siderophore production assays, two representatives of Atlantic salmon isolates and the seal type strain were examined. All of them were able to utilize apo-transferrin, transferrin hemin, hemoglobin, ferric ammonic citrate and ferric chloride as iron sources when added to iron-deficient media; although S. phocae possesses a stronger capacity for iron acquisition from hemoglobin than hemin. Whole cells of all S. phocae strains, grown under iron-supplemented or iron-restricted conditions were able to bind hemin, indicating the existence of constitutive binding components located at the S. phocae cell surface. In all strains, at least two iron-regulated membrane proteins increased when S. phocae was cultured in iron-restricted medium. Iron did not play a regulatory role in the synthesis of some proteolytic enzymes and hydrophobic properties, since these activities were similar when the strains were cultured in iron-rich or iron-restricted conditions.
Julio Retamales, Alberto González-Contreras, Soraya Salazar, Alicia E. Toranzo, Ruben Avendaño-Herrera

This study evaluated the ability of the disc diffusion protocols and epidemiological cut-off values published by the Clinical and Laboratory Standards Institute (CLSI) to detect sul1 containing strains of Aeromonas salmonicida. Molecular analysis of sixteen strains demonstrated the presence of sul1 in seven of them. Two sets of disc diffusion data for these sixteen strains, produced in two studies preformed five years, apart, were used in the evaluation. Data sets produced using a disc containing both sulfamethoxazole and trimethoprim, as recommended by CLSI, were analysed using the recommended epidemiological cut-off value. When this cut-off value was applied to the data generated in the first study, fifteen of the sixteen strains were categorised as wild-type. When it was applied to the data generated in the second study, all sixteen strains were categorised as wild-type. When the strain susceptibilities were investigated using discs that contained 100μg sulfamethoxazole only, strains that were sul1 negative manifested zones ≥18mm in one study and ≥24mm in the other. None of the sul1 containing strains manifested any zones of inhibition in either study. A provisional epidemiological cut-off value (≥9mm) has been suggested for sulfamethoxazole disc data generated under the test conditions specified by CLSI. Evidence is presented that it is highly likely that application of this cut-off value to such data would lead to the categorisation of all sul1 negative strains as wild type and all sul1 containing strains as non-wild type. It is argued that, in order to maximise their ability to detect the presence of sul1 containing strains, standardised monitoring and surveillance programmes should adopt protocols that specify the use of discs containing only sulfamethoxazole.
Elizabeth Minogue, Thomas Barry, Cyril Carroll, Peter Smith

Genetic selection is being developed as a management tool for the control of amoebic gill disease (AGD) in Atlantic salmon. AGD is caused by an external gill parasite and is an animal health issue that results in significant economic loss to the Tasmanian salmon industry. This paper presents genetic parameters for AGD resistance, describes patterns of genetic variation over multiple infection cycles, and discusses the development of a selective breeding program to exploit this variation. Measurements of visible gill signs were made on over 12,000 individuals representing 326 sires and 297 dams from four genetically linked year classes. Between three and six sequential infections were measured on each year class. All measures of gill signs in all year classes had significant genetic variation with heritabilities ranging from 0.09±0.03 to 0.56±0.07. Genetic correlations between infections indicate two distinct traits which are only weakly correlated (average rg =0.24). One is measured at first infection on naïve fish and the other can be measured at all subsequent infections. This pattern is suggestive of an adaptive immune response for reinfections, and conforms with patterns seen for resistance to other parasitic diseases in terrestrial livestock. In an analysis combining all year classes, the heritability for first infection was 0.14±0.02 and heritabilities for reinfections ranged from 0.23±0.08 to 0.40±0.03. Reinfections appeared to be mostly under common genetic control, although there appear to be additional genetic traits that cause lower correlations for a small proportion (about 10%) of the population. Consistent and stable patterns of inheritance are indicated by the medium to high genetic correlations between year classes and by the high genetic correlations between infection cycles with a seasonal shift. Estimation of genetic correlations between AGD resistance and growth rate are problematic due to confounding effects but it is likely that this correlation is near zero. Selection for AGD resistance can assist with disease management and is part of the breeding objective of the Tasmanian salmon breeding program. Adaptive AGD resistance is one of the primary selection traits and a field challenge based on assessment of gill signs is an effective way of selecting for resistance. The current selective breeding strategy is predicted to increase the interval between treatments by 3% per year.
Peter D. Kube, Richard S. Taylor, Nicholas G. Elliott