Ability of Electric Field Strength, Frequency, and Current Duration to Stun Farmed Atlantic Salmon and Pollock and Relations to Observed Injuries Using Sinusoidal and Square Wave Alternating Current

Abstract

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.