Ethical slaughter of fish: Practices from large-scale production of Atlantic salmon. Past, present and future slaughter methods

Ulf Erikson

SINTEF Fisheries and Aquaculture, 7465 Trondheim,  Norway



During the past few decades, the salmonid fish farming industry in Norway has experienced a tremendous growth in biomass production. At harvesting, well-boats transport live fish from the rearing cages to fish processing plants. Previously, carbon dioxide was added at high concentrations to stunning tanks, often overcrowded, causing excessive handling stress. RSW live chilling was eventually introduced prior to carbon dioxide stunning. As this option was not entirely successful, carbon dioxide was then added at lower concentrations directly to the live chilling tank. This is the common stunning method today. Subsequently, the gill arches are severed and the fish are bled in an RSW tank. From a fish welfare point of view, the current stunning method (combining live chilling and carbon dioxide) may not be considered as an optimal stunning method since the fish are not rendered unconscious immediately. Thus, the fish may experience considerable stress or pain. Therefore, optimizing sedation and killing methods of farmed fish (salmonids and cod) are currently major issues to comply with customer demands and future legislation related to animal welfare. To assess fish welfare and handling stress, a number of indicators may be used: behaviour, changes in blood composition (whole blood or plasma constituents) and parameters related to fish product quality (biochemistry of the muscle). In current projects, we plan to evaluate various slaughter methods: RSW live chilling combined with mild carbon dioxide anaesthesia (current slaughter method for salmonids), eugenol (AQUI-STM), percussion stunning (blow to the head) and electrical stunning. Major evaluation criteria are fish welfare, handling stress, bleeding efficiency and time to rigor onset.