Enriched rearing environment and wild genetic background can enhance survival and disease resistance of salmonid fishes during parasite epidemics.
The importance and volume of aquaculture is increasing world-wide. Rearing practices play a key role in determining growth rate, survival and disease resistance in aquaculture fishes. Recent evidence suggests that in comparison with a standard stimulus-poor rearing environment, an enriched or variable rearing environment has significant positive effects on several traits underlying growth and well-being of fish. However, the effect of enriched rearing on one of the most important threats for aquaculture development, occurrence of parasitic infections, remains unknown. We used surveillance data of experimental salmonid populations of wild and hatchery origin under semi-natural parasite exposure to explore effects of enriched rearing on outbreaks of important aquaculture pathogens and associated fish mortalities in production-scale fish densities. We also conducted controlled parasite exposures to investigate if enriched rearing reduces susceptibility of fish to infection in comparison with standard rearing conditions. We found evidence of enriched rearing influencing survival and disease resistance of aquaculture fish during parasite epidemics. Essentially, populations from enriched rearing had a higher survival rate, lower parasite occurrence and greater resistance to most infections compared to fish held in standard rearing conditions. Similarly, fish of wild genetic background had lower mortality during some of the epidemics compared to fish of hatchery origin. However, we also demonstrate significant variation in these patterns and in some cases a tendency for opposite effects of enriched rearing and genetic background depending on the fish species and nature of the epidemic. Synthesis and applications. Our results suggest that parasitic infections and epidemics can be managed through enriched rearing conditions. This may have important implications for economically and ecologically sustainable parasite and disease prevention strategies in aquaculture.