Managing Infectious Disease Risks in Salmon and Steelhead Hatcheries and Natural Populations

Much success has been achieved in controlling disease in Pacific salmon and steelhead hatcheries. Many good health practices have been adopted when possible, including improved animal husbandry, enhanced biosecurity measures, regular disease inspections, judicious use of chemotherapeutics, and vertical transmission control. Our knowledge of finfish diseases is largely based on studies of cultured fish and we know comparatively less about diseases in natural populations. In this presentation, I will review some potential risks that hatchery populations may pose to natural populations. For instance, hatchery rearing can facilitate pathogen amplification which, if released, may pose a risk to nearby populations. Similarly, novel host or environmental conditions encountered in the hatchery setting, as well as specific fish management practices, may theoretically drive evolution and possibly alter virulence. The practice of moving fish may introduce pathogens into new geographical areas, with potentially devastating effects on naïve populations. However, much can be done to reduce the risk of hatcheries to natural populations. For instance, the use of local fish stocks in conservation hatcheries reduces the risk from introduction of exotic pathogens and local stocks may be better able to resist endemic pathogens.