Studies of risk factors associated with proliferative gill inflammation in seawater-reared Atlantic salmon

Proliferative gill inflammation has been detected for at least 15 years in Atlantic salmon but the disease is still poorly characterized. The prevalence and mortality rates caused by the gill disease seem to be increasing and this is an obstacle in Norweg ian aquaculture. The infectious agent(s) is/are not known with certainty and the aetiology is apparently multifactorial including infection with intracellular chlamydia-like organsims, Atlantic salmon paramyxovirus and protozoan ectoparasites. As the infe ctious agents remains undefined, medication and vacciantion are not feasible and preventive measures taken so far against this disease have proven insufficient. Several factors always contribute to any disease pattern, and in spite of unknown infectious a gents, intervention throught other factors (management, hygiene, environment, etc.) may still reduce the disease problems. In order to expand the knowledge of the disease and possibly identify intervention strategies that can prevent spreading of the dis ease, decrease mortality and the loss of appetite in survivors, the project will focus on an epidemiological approach exploiting existing and prospective data gathered by the farming industry.