Abstract
Spontaneous mortality of seemingly healthy, farmed Atlantic salmon ( Salmo salar L) is an increasing problem in Norwegian aquaculture. In this study, we present a morphological study of the previously undescribed syndrome of arteriosclerosis of the ventral aorta and epicarditis of the adjacent bulbus arteriosus found in farmed Atlantic salmon, with wild‐captured fish as a control group. Both the ventral aorta and epicardium are vital for correct arterial compliance and vascular resistance in the respiratory capillaries of the gills. We discuss the possible implications of ventral aorta arteriosclerosis and epicarditis for blood vascular health and in particular for the increasing frequency of spontaneous gill bleeding in farmed salmon. As both these conditions primarily occur in farmed salmon, we suggest that they should be considered pathological.