Comparing the effects of high vs. low nitrate on the health, performance, and welfare of juvenile rainbow trout Oncorhynchus mykiss within water recirculating aquaculture systems

•Juvenile rainbow trout health and performance was compared between high vs. low nitrate conditions in recirculating systems.•A significantly greater prevalence of “side swimming” rainbow trout was quantified for the high nitrate treatment.•Slightly slower growth and decreased survival resulted in significantly lower fish biomass for the high nitrate treatment.•High nitrate nitrogen (80–100mg/L) was related to chronic health and welfare impacts to juvenile rainbow trout.