Live chilling of Atlantic salmon (Salmo salar) combined with mild carbon dioxide anaesthesia. I. Establishing a method for large-scale processing of farmed fish

The goal of the present study is to evaluate the combined effect of live chilling and carbon dioxide narcosis as a potential stunning/chilling method for Atlantic salmon in a commercial slaughter line. Water quality parameters in cage and RSW tanks, handling stress (white muscle pH), body temperature profile as affected by processing, rigor mortis development, and fillet quality (protein and textural properties, fillet pH and colour) after ice storage for 1 and 2 weeks, were evaluated. Fish from sea cage, live chilling RSW tank and carbon dioxide stunning RSW tank were compared. Effects of pumping and live chilling on blood vessels in gill arches were also evaluated. Under the prevailing slaughter conditions, it was shown that by using live chilling with a deltaT (SW vs. RSW) of 8-10 °C, oxygen levels (60-156% saturation) and moderate carbon dioxide levels (37-80 mg l-1), it was possible to process Atlantic salmon without inflicting excessive handling stress. Consequently, the fish exhibited a long pre-rigor period (about 24 h) giving ample time for pre-rigor processing. Moreover, no detrimental effects on blood vessels in gills and fillet quality were observed, i.e. the processed fish were not different from the fish taken directly from sea cage. The proposed stunning method of combining live chilling and moderate levels of carbon dioxide in a single tank was considered to be superior to the traditional carbon dioxide stunning method using very high levels of carbon dioxide in a comparatively small tank.