Abnormal swimming behavior and increased deformities in rainbow trout Oncorhynchus mykiss cultured in low exchange water recirculating aquaculture systems

► Rainbow trout within low exchange WRAS exhibited increased swimming speeds and greater incidence of “side swimming” behavior. ► Increased deformities, mortality, and unusual swimming behaviors were observed within near-zero exchange WRAS. ► Of the parameters assessed, nitrate nitrogen and/or dissolved potassium could have caused the observed problems.