RISK-FACTORS FOR FURUNCULOSIS, INFECTIOUS PANCREATIC NECROSIS AND MORTALITY IN POST-SMOLT OF ATLANTIC SALMON, SALMO-SALAR L

An epidemiological longitudinal study comprised information obtained f rom 124 randomly selected Norwegian sea-sites housing post-molts of At lantic salmon, Salmo salar L. Information on crude cumulative mortalit y, fish characteristics and farm factors was gathered by the veterinar y practitioners servicing the farms. The observation period lasted fro m the time of sea transfer of the smolts in the spring until 1 October 1991. On average, 116 480 smolts were transferred to each sea-site. T he mean crude cumulative mortality of post-smolts during the period co ncerned was 16.8%. The cumulative farm-level incidence was 54.0% for f urunculosis, 39.5% for infectious pancreatic necrosis (IPN) and 10.5% for vibriosis. Occurrence of any of these specific infectious diseases in the post-smolt was significantly associated with mortality. The ri sk of furunculosis was significantly related to the location of the se a site. Mixing of smolt from many freshwater hatcheries in the sea far m increased the risk of IPN significantly. In addition, the risk of IP N was related to age of site and geographic location. The mean cumulat ive mortality in 1-year-old smolt groups was 17.5%, significantly grea ter than in two-year-old fish (7.9%). In addition, the method used to transport fish from the freshwater hatchery to the sea site was signif icantly associated with mortality. Neither the weight of smolts at sea transfer nor the date of transfer were significantly related to morta lity.