Effect of carbon monoxide on welfare and quality in Atlantic salmon (Salmo salar L.)

Carbon monoxide (CO) has been used as a food preservative in the food industry. CO can be used to sedate, anaesthetize or kill animals without aversive reactions. The early application of CO in the slaughtering process seems to be beneficial by giving a more red stable colour, reducing microbial growth and lipid oxidation; this would be preferable for salmon which is highly vulnerable to lipid oxidation due to the high level of unsaturated fatty acids. Atlantic salmons (Salmo salar L.) were used to evaluate CO effects on shelf life and welfare. Fish were exposed to CO for 8 (CO8) and 20 minutes (CO20) and compared to stressed (SF) or control (C) groups. All fish were hauled from the tank and killed by percussion. Plasma Adrenaline and Noradrenaline contents were measured as stress indicators. Fish exposed to CO8 showed no stress signals, whereas Adrenaline content was significantly higher in CO20. The C and SF fish showed a lower catecholamine level than CO20. This reflects a challenge when conducting field studies with regard to stress. CO treatment affected positively colour and favoured a rapid onset of rigor mortis and a small but significant increase in drip loss.