Pathological pigmentation in cardiac tissues of Atlantic salmon (Salmo salar L.) with cardiomyopathy syndrome

It is widely accepted that melanin formation may play an immunologic role in invertebrates and ectothermic vertebrates. In farmed Atlantic salmon, cardiomyopathy syndrome (CMS) is a common viral disease associated with severe cardiac inflammation that may be accompanied by heavy melanisation of the heart. By the use of histology, laser capture microdissection and transcription analysis of tyrosinase genes, we here show that this melanisation is linked to de novo melanogenesis by melanomacrophages, suggesting an active part in the inflammatory reaction. No general systemic activation of the extracutaneous pigmentary system in response to viral infections with affinity to the heart was observed.