Isoeugenol (17 mg AQUI-S™ L⁻¹), nitrogen, and three levels of carbon dioxide (low: 70-80, medium: 180-250 and high: > 400 mg CO₂L⁻¹) were tested as stunning agents for Atlantic salmon(Salmo salar)fasted for six days. All methods were tested under optimised conditions (starting with rested fish, and stunning and recovery under good water quality conditions). The fish were assessed in relation to behaviour and stress in terms of blood chemistry and muscle biochemistry. Only isoeugenol fulfilled all of our set criteria related to fish welfare and stress as it: (i) minimised aversive reactions upon exposure and ability to render the fish unconscious; (ii) showed no recovery during a period of 10 min post stunning; and (iii) achieved minimal muscle activity (good muscle quality). The fish treated with nitrogen showed the strongest aversive reactions, produced the most stressed fish, and fish that did not appear to be sedated. Nitrogen stunning cannot therefore be recommended. None of the levels of carbon dioxide fulfilled all criteria. When exposed to high and medium levels, fish exhibited aversive reactions and became considerably stressed. At the low level, changes in behaviour and stress were modest, but in such cases the fish were not sufficiently immobilised to facilitate easy handling in a possible pre-stunning context. No level of carbon dioxide rendered the fish unconscious. Even under optimised stunning conditions, the use of carbon dioxide cannot be recommended in connection with slaughter of Atlantic salmon.

Gutted Atlantic cod, packed in cartons, were frozen immediately after killing in a magnetic field (cell alive system). The results were compared with traditional air-blast freezing or by putting the cartons directly in a cold storage room (without forced convection of air). After frozen storage, external and fillet properties were compared. In spite of differences in freezing rates, only minor differences were found among treatments. The mechanism for the freezing of fish in the magnetic field, under the current conditions, appeared to be similar to that of traditional freezing methods.

Eleven commercial processing lines for the slaughter of Atlantic salmon were evaluated to investigate the efficiency of the refrigerated seawater live chilling method with respect to stunning fish and reducing body temperature. The method is commonly used in the Norwegian salmon industry to both stun and chill fish before killing. Carbon dioxide gas was added to the live chilling tanks, or in some cases, to a subsequent carbon dioxide stunning tank. Criteria used for evaluation were water quality parameters (dissolved oxygen, carbon dioxide, pH, temperature, total ammonium, ammonia, alkalinity, color, total organic carbon, and ferric ion), fish behavior, white muscle pH, and body and core temperatures. At two processing plants, fillet quality (Roche color, texture, ultimate pH, and water content) was also determined. The results are discussed in terms of fish acclimation temperatures, water quality, welfare, handling stress, chilling efficiency, pre-live chilling factors, refrigerated seawater live chilling process parameters, and fillet quality. Even though the live chilling method can be used to minimize fish handling stress during slaughter and may serve as an efficient chilling method, it was found in most cases that under commercial conditions when large biomasses were slaughtered, both handling stress and chilling efficiency were less than optimal. However, no adverse effects on the fillet texture and color were observed as a result of fish processing.