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

Abstract

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