Abstract
High pre-slaughter mortality rates of Atlantic salmon (Salmo salar L.) are a reoccurring welfare issue and economic burden in aquaculture. Sudden death immediately prior to slaughter is particularly problematic given the considerable resources invested to reach this stage. Although the underlying causes of such mortality are largely unknown, cardiac deformities and diseases have become increasingly prevalent observations in deceased fish. The factors leading to this pathology remains to be revealed. Thus, we presently examined if intensive smolt production and concordant fast growth rates in young fish is associated with altered cardiac morphology at later production stages in Atlantic salmon. The observed alterations were subsequently related to mortality risk following de-lousing in a facility with a cardiomyopathy syndrome (CMS) outbreak.We observed that intensive smolt production is indeed associated with slower growth rates at sea, distinct pathological cardiac morphological alterations, and expression of cardiac pathology markers. Moreover, the observed cardiac alterations co-occurred with CMS-related cardiac rupture at a different production facility. The present study demonstrates a clear link between pace of growth at early rearing stages and cardiac deformities later in life. Furthermore, these cardiac deformities are associated with cardiac rupture and mortality in individuals with CMS during delousing. We therefore believe that a slower pace of smolt production improves cardiac health and reduces the risk of mortality during CMS outbreaks.
Highlights
The biology of Atlantic salmon (Salmo salar) attracts growing research interest due to its complex life history and great economic importance for the aquaculture industry (Brocklebank and Raverty, 2002; Kongtorp et al, 2006; Kittilsen et al, 2009; Kittilsen et al, 2012; Vindas et al, 2016; Wessel et al, 2017)
We found that fast smolt production is associated with slower growth rate at sea, distinct cardiac morphological deviations, and higher expression of the cardiac stress marker atrial natriuretic peptide and the angiogenesis marker vascular endothelial growth factor
Fast and slow smolt production groups To test the hypothesis that conditions under smolt production are related to deviating heart morphology later in life, two groups of Atlantic salmon reared at the same commercial sea farm (Korsnes, Ellingsen seafood AS, 68°19'53.3"N 14°56'53.6"E) were sampled in October 2019
Summary
The biology of Atlantic salmon (Salmo salar) attracts growing research interest due to its complex life history and great economic importance for the aquaculture industry (Brocklebank and Raverty, 2002; Kongtorp et al, 2006; Kittilsen et al, 2009; Kittilsen et al, 2012; Vindas et al, 2016; Wessel et al, 2017). More than 50 million Atlantic salmon die annually during the seawater stage in Norwegian aquaculture alone (Grefsrud et al, 2018). This mortality results in annual economic losses exceeding 1.5 billion USD. During recent years loss of fish just prior to slaughter has emerged as an increasing cause of production losses (Grefsrud et al, 2018). CMS is one of the leading causes of morbidity and mortality in the salmon aquaculture industry and has been estimated to affect up towards 20 % of all fish in affected sea cages (Garseth et al, 2018). There is no vaccine, cure or treatment for CMS and with rising prevalence, the economic burden of this disease may become unmanageable
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