Macro- and microparasite infection profiles of hatchery fish before and after release from a conservation hatchery (steelhead trout, Oncorhynchus mykiss)

Abstract

Conservation hatcheries are becoming a tool in rebuilding salmonid populations, but their contributions are strongly debated. Most studies focus on genetic, morphological, and behavioural, issues and less is known of the importance of infectious agents. The Living Gene Bank (LGB) program of the British Columbia Ministry of the Environment is a recent effort to restore collapsed steelhead trout (Oncorhynchus mykiss) populations on the east coast of Vancouver Island. Our study describes the change in macro- and microparasitic profiles of LGB-hatchery-produced juveniles after they leave the hatchery and enter the natural river environment and also compares them with a limited wild smolt sample. We found that the hatchery was successful in raising parr free of infectious agents, but once introduced into the river environment, the hatchery fish quickly took on a diverse profile of infectious agents. The high numbers of fish released from the hatchery and the existence of hatchery fish that stay in the river as residents increased the number of fish in the system with sub-clinical levels of infection. An ecological understanding of the role resident hatchery fish play in the spatial distribution of infectious agents as well as the temporal and seasonal variations in infectious agent prevalence and diversity will be important in determining the net effect of the LGB conservation hatchery on the wild population.