Diseases and parasites in wild Atlantic salmon (Salmo salar) populations

The ecology of infectious diseases in wild and managed salmon populations i s reviewed. Few pathogens have caused significant disease epidemics in the wild, and although parasites of returning adults are best documented, disea ses among parr (e.g., Gyrodactylus salaris) are probably most important. Th e greatest diversity of parasites is known from the marine phase but few ar e likely to be significant pathogens, although conclusive evidence is lacki ng because diseased salmon cannot be tracked. The importance of stress as a n immunosuppressant of fishes in degraded habitats is discussed. In additio n, releases and restocking have probably also reduced the genetic disease r esistance of wild fishes. We note that myxozoans, furunculosis, G. salaris, and sea lice are the pathogens most likely to threaten wild and managed sa lmon stocks in future. Despite abundant research on pathogens of farmed sal mon, little is known of their impact on wild or managed stocks and an adequ ate theoretical framework for salmon disease epidemiology is urgently neede d before disease becomes a limiting factor in salmon conservation.