Susceptibility of genotyped marble trout Salmo marmoratus (Cuvier, 1829) strains to experimental challenge with European viral haemorrhagic septicemia virus (VHSV) and infectious hematopoietic necrosis virus (IHNV)

The marble trout Salmo marmoratus (Cuvier, 1829) is an endemic species of great conservation concern, given its geographical restricted distribution and the high risk of hybridization with brown trout Salmo trutta L. Viral hemorrhagic septicemia (VHS) and infectious hematopoietic necrosis (IHN) are predominantly diseases of freshwater salmonids, which may trigger off severe disease outbreaks causing high mortality. Marble trout has not been inserted in the vector species list for those pathogens, but at present, little information on its susceptibility and on the possible carrier status is available. The aimof the present study was to assess the ability of European strains of VHSV and IHNV to cause disease and associated mortality in experimentally infected marble trout, and to determine whether a carrier status can result after experimental infection. Three genetically different strains of marble trout were challenged with VHSV and IHNV by immersion. Rainbow troutswere used as positive controls. Fish were checked twice a day, and dead fish were removed and sampled for subsequent virological analyses. With respect to rainbow trout, results demonstrated a very low susceptibility of marble trout to both VHSV and IHNV under simulated natural conditions. The presence of a certain number of chronically infected marble trout confirms that some individuals can survive the infection and eventually act as carrier of the disease, suggesting that marble trout should be definitely added to the list of susceptible species according to the European legislation.