Immune response in rainbow trout against infection with Flavobacterium psychrophilum

The fish pathogen Flavobacterium psychrophilum is one of the main causes of mortality in farmed rainbow trout and other salmonid fish. An infected farm can expect mortality rates around 50-60% in fry and 2-10% in juvenile fish within few weeks. Presently no commercial vaccine exists, and fish farmers control the disease with antibiotics. The pathogen has a limited ability to cause disease in an experimental setting without applying a stressor. A bath-model using 150mg/L H2O2 for 60 minutes as a stressor was used on 1.4g rainbow trout fry in four experimental groups: 1) no H2O2/no bath infection, 2) H2O2/no bath infection, 3) no H2O2/ bath infection and 4) H2O2/ bath infection. Bath infections were carried out in 107 CFU/ml F. psychrophilum bath solution and control groups were bathed in sterile medium. Samples from all internal organs, head and skin were taken before pathogen exposure and 4 hours, 2 days, 5 days, 8 days and 17 days after exposure. The samples will be used for examining the gene expression in rainbow trout related to infection with F. psychrophilum and results will be presented. Furthermore, antibody production will be assessed using ELISA on serum samples. The results will be used in order to optimize vaccination or immune-stimulation.