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Trial Lecture – time and place
See Trial Lecture.
Adjudication committee
- First opponent: Assistant Professor Bjarke Jensen, Amsterdam UMC, Netherlands
- Second opponent: Associate Professor Aase Beathe Mikalsen, Norwegian University of Life Sciences (NMBU)
- Third member and chair of the evaluation committee: Professor Shuo-Wang Qiao, University of Oslo
Chair of the Defence
Associate Professor Jan Magnus Aronsen, University of Oslo
Principal Supervisor
Postdoctoral Fellow Michael Frisk, University of Oslo
Summary
Norwegian Atlantic salmon aquaculture represents a large-scale industry with consistent high mortality rates. Among multiple biotic and abiotic causes, cardiac pathology is a major contributing factor. Deviating cardiac morphology, such as rounded or skewed ventricles, has gained increasing attention, while infection with piscine myocarditis virus (PMCV), causing cardiomyopathy syndrome (CMS), remains a persistent source of mortality. However, limited studies have examined how these conditions affect cardiac function, partly due to a lack of rapid, non-invasive assessment methods.
This thesis aimed to develop echocardiographic protocols for non-invasive evaluation of cardiac morphology and function, and to determine how these are altered by deviating morphology and PMCV infection in farmed Atlantic salmon. Echocardiography proved effective, producing functional and morphometric measurements comparable to invasive techniques. Combined with intraventricular pressure measurements, this approach demonstrated that both conditions alter systolic function, primarily through increased stroke volume and contractility. In addition, PMCV infection results in elevated intraventricular pressure and altered diastolic function.
Both conditions appear to involve compensatory functional changes at rest, suggesting reduced cardiac reserve and increased susceptibility to mortality under production stressors such as crowding, delousing, and transport. Histopathological analyses revealed distinct remodelling patterns: deviating morphology was associated with focal thickening of the ventricular compact layer and atrial enlargement, whereas PMCV infection induced concentric thickening via hyperplasia. Fish that succumbed during delousing exhibited hypertrophic myocardium and more severe cardiac lesions than survivors, indicating that hyperplastic growth may represent a survival phenotype.
Overall, this work advances understanding of two major cardiac conditions that are linked to mortality in farmed Atlantic salmon and may support improved disease detection (e.g., biomarker development), prevention, and treatment strategies.
Additional information
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