Arnfinn Aunsmo

Association of spinal deformity and vaccine-induced abdominal lesions in harvest-sized Atlantic salmon, Salmo salar L.

Spinal deformities in Atlantic salmon, Salmo salar L., have been described as a disease of multifactorial origin for which vaccines and time of vaccination have been suggested as risk factors. A vaccine efficacy trial where spinal deformity became evident was continued by the observational study reported here. In the preharvest part of the study 17 months post-sea transfer, there was a prevalence of 11.3% spinal deformity, with deformities present only in one vaccine group indicating a strong vaccine involvement. At slaughter, the prevalence of spinal deformities was 11.7%, and deformed fish had only 62% of normal slaughter weight. Visual analogue scales (VAS) were used for continuous recordings of vaccine-induced abdominal lesions and deformity. A logistic regression model associating presence of spinal deformity with markers of abdominal lesions was developed. The odds ratio for spinal deformity was 5.7 (95% CI: 3.4-9.4) for each unit increase in adhesion score (0-6) and 4.9 (2.9-3.4) for each unit increase in melanin on abdominal organs (0-3). Lesions in the dorsal caudal part of the abdomen gave an odds ratio for spinal deformity of 2.2.

Stochastic modelling of direct costs of pancreas disease (PD) in Norwegian farmed Atlantic salmon (Salmo salar L.).

An economic model for estimating the direct costs of disease in industrial aquaculture was developed to include the following areas: biological losses, extraordinary costs, costs of treatment, costs of prevention and insurance pay-out. Direct costs of a pancreas disease (PD) outbreak in Norwegian farmed Atlantic salmon were estimated in the model, using probability distributions for the biological losses and expenditures associated with the disease. The biological effects of PD on mortality, growth, feed conversion and carcass quality and their correlations, together with costs of prevention were established using elicited data from an expert panel, and combined with basal losses in a control model. Extraordinary costs and costs associated with treatment were collected through a questionnaire sent to staff managing disease outbreaks. Norwegian national statistics for 2007 were used for prices and production costs in the model. Direct costs associated with a PD-outbreak in a site stocked with 500,000 smolts (vs. a similar site without the disease) were estimated to NOK (Norwegian kroner) 14.4 million (5% and 95% percentile: 10.5 and 17.8) (NOK=euro0.12 or

Methods for investigating patterns of mortality and quantifying cause-specific mortality in sea-farmed Atlantic salmon Salmo salar

0.17 for 2007). Production was reduced to 70% (5% and 95% percentile: 57% and 81%) saleable biomass, and at an increased production cost of NOK 6.0 per kg (5% and 95% percentile: 3.5 and 8.7).

Modelling salmon lice, Lepeophtheirus salmonis, reproduction on farmed Atlantic salmon, Salmo salar L.

Methods for investigating patterns of mortality and quantifying cause-specific mortality in Atlantic salmon Salmo salar farming were developed. The methods were further used to investigate mortality and patterns of mortality for the first 3 mo after sea transfer in the 2006 year-class autumn smolts (SO) of Norwegian farmed Atlantic salmon. In the study population, which consisted of 20 pens at 10 sites, cause-specific mortality was examined by 11 fish health professionals during 8 visits to each pen. Cause-specific mortality proportions were used to convert crude mortality into cause-specific mortality. Cumulative mortality in the study period was 2.1% in the study population compared with 3.7% for the 2006 year-class SOs in the national database. Of this cumulative mortality, 73 and 59% took place in 20% of the pens in the study and the reference population, respectively. Daily mortality rates in the study population showed a variation from 0 to 2376 per 100,000 fish where the majority of mortality was observed during disease outbreaks. All study pens had periods of low baseline mortality and some pens had no increased mortality during the study period. Of 2088 dead fish examined, 92% (1929 fish) were assigned a specific cause of death, and in 97% of these 1929 fish the investigators reported the given cause of death to be likely or very likely. Ulcers were the main cause of death, accounting for 43% of the assigned mortality, and infectious agents were involved in 64% of the total mortality. The study shows that probable causes of death can be established in Atlantic salmon farming and their contribution to total mortality measured.

Associations between piscine reovirus infection and life history traits in wild-caught Atlantic salmon Salmo salar L. in Norway

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.

Impacts of parasites on marine survival of Atlantic salmon: a meta-analysis

Piscine Reovirus (PRV), the putative causative agent of heart and skeletal muscle inflammation (HSMI), is widely distributed in both farmed and wild Atlantic salmon (Salmo salar L.) in Norway. While HSMI is a common and commercially important disease in farmed Atlantic salmon, the presence of PRV has so far not been associated with HSMI related lesions in wild salmon. Factors associated with PRV-infection were investigated in returning Atlantic salmon captured in Norwegian rivers. A multilevel mixed-effect logistic regression model confirmed clustering within rivers and demonstrated that PRV-infection is associated with life-history, sex, catch-year and body length as a proxy for sea-age. Escaped farmed salmon (odds ratio/OR: 7.32, p<0.001) and hatchery-reared salmon (OR: 1.69 p=0.073) have higher odds of being PRV-infected than wild Atlantic salmon. Male salmon have double odds of being PRV infected compared to female salmon (OR: 2.11, p<0.001). Odds of being PRV-infected increased with body-length measured as decimetres (OR: 1.20, p=0.004). Since body length and sea-age are correlated (r=0.85 p<0.001), body length serves as a proxy for sea-age, meaning that spending more years in sea increases the odds of being PRV-infected.