Sixteen specimens of female crucian carp, Carassius carassius (L.), during the breeding season, were investigated for post-mortem and full diagnostic examination during a mortality outbreak in a tributary stream of the Arno River in Tuscany in 2011. Necropsy highlighted the presence of a swollen anus and widespread haemorrhages in the body, fins, gills and eyes. Haemorrhages in internal organs and spleen granulomas were also observed. Bacteria isolated from the brain, kidney and spleen of affected fish were identified as A. sobria. Microscopic lesions observed in gills were characterized by necrosis of the secondary lamellae, congestion and multifocal lamellar fusion. The kidney showed necrosis, oedema, fibrin exudation and areas of haemorrhages, while in the spleen the main lesions were by multifocal necrosis of the lymphoid tissue. In the gills, transmission electron microscopy revealed herpesvirus-like particles, subsequently identified as Cyprinid herpesvirus-2 (CyHV-2) with a nested PCR protocol. Although it was not possible to attribute a pathogenic role to CyHV-2 in this mortality event, the identification of this herpesvirus in crucian carp increases the concern about its potential role in this species.

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