Shear force and rigor mortis were used to evaluate the post-mortem changes of muscle texture in Atlantic salmon (Salmo salar). The fish were either stunned with carbon dioxide (CO 2 ), electricity, or percussion prior to slaughter. The pre-mortem stress during CO 2 stunning resulted in an earlier onset and resolution of rigor mortis, and accelerated post-mortem softening of the muscle tissue as compared to the other stunning methods. No significant differences, either in development of rigor mortis or shear force, were seen between fish that were stunned with electricity or by percussion. Consequently electricity can be used for stunning fish prior to slaughter.

We evaluated electricity as a stunning method before slaughter of Atlantic salmon Salmo salar by assessing both stunning effectiveness and injuries. About 300 salmon (1.2-6.6 kg) were exposed to one-phase, sinusoidal, 50-Hz AC in seawater; electrical field strengths ranged from 15 to 250 V/m and current durations from 0.2 to 12 s. We measured the duration of the epileptic-like seizures after stunning and the degree of unconsciousness based on behavioral responses. Fish were killed, bled, and gutted 10 min after stunning and then analyzed for injuries. The proportion of fish sufficiently stunned, the duration of an unconscious condition, and the occurrence of broken vertebrae and hemorrhages were all dependent on electric field strength and current duration. The electric field strength required to stun the fish was inversely proportional to the current duration, dropping from 200 V/m at 0.8 s to 25 V/m at 6-12 s. Electricity proved to be efficient in stunning fish, but to avoid injuries in market-sized Atlantic salmon the current duration should be less than 1.5 s at field strengths ranging from 125 to 150 V/m.

The effects of electricity as a stunning method in the slaughtering process of Atlantic salmon Salmo salar and pollock Pollachius virens were studied. About 330 slaughter‐sized Atlantic salmon were exposed to sinusoidal alternating current (AC) in seawater. Electrical field strength ranged from 25 to 100 V/m and current duration from 1 to 10 s at frequencies between 30 and 2,000 Hz. In addition, 122 pollock and 25 salmon were stunned by applying square wave AC in the range of 50–1,000 Hz. After stunning, subsequent unconsciousness was evaluated by means of behavioral responses, and injuries were observed by examining fillets. For sinusoidal AC, the proportion of Atlantic salmon sufficiently stunned and the occurrences of obviously broken spinal columns and hemorrhages were dependent on the electrical frequency used. The AC frequency was the most predominant factor in both stunning and inflicted injuries. The proportion of injured salmon exhibited a unimodal response to sinusoidal AC frequency, increasing from 30 Hz to 50– 80 Hz and declining with higher frequencies. There was not a consistent injury‐versus‐frequency pattern for pollock exposed to square wave AC. For Atlantic salmon, use of square wave AC did inflict a higher rate of injuries than that of sinusoidal AC. For minimizing the occurrence of injuries while sustaining sufficient stunning before slaughter, sinusoidal AC frequencies between 500 and 1,000 Hz are recommended at field strengths exceeding 50 V/m and current durations of 10 s.