Handling procedures including sampling, vaccination, and transport cause significant stress in farmed fish. Anesthetic use before handling dramatically reduces physiological stress responses and improves fish welfare outcomes.
Fish anesthesia is an underutilized welfare tool in aquaculture that provides clear benefits with minimal risk when properly administered. Handling without anesthesia causes acute physiological stress measured through cortisol, glucose, and lactate elevation that persists for hours to days, affecting immune function and potentially increasing disease susceptibility. Vaccination without anesthesia causes both the stress of handling and pain from injection while fish struggle. With anesthesia, fish are sedated before handling, vaccination proceeds quickly without struggling, and recovery is rapid. The economic case includes better vaccine efficacy and reduced secondary disease from handling stress. Regulatory requirements for anesthesia use before specified procedures, as implemented in Norway, represent welfare progress that should be extended to more species and procedures globally.