This study investigated the effects of three microscreen mesh sizes (100, 60 and 20 m) on water quality and rainbow trout (Oncorhynchus mykiss) performance compared to a control group without micro-screens, in triplicated recirculating aquaculture systems (RAS). Operational conditions were kept constant during a 6-week period where the microscreens were manually rinsed three times a day. The effects of microscreen cleaning frequency and nitrification performance were subsequently assessed.