Percussion and electrical stunning of Atlantic salmon (Salmo salar) after dewatering and subsequent effect on brain and heart activities

The overall objective of the study was to evaluate a percussive and an electrical stunning method under laboratory conditions in Atlantic salmon. Evidence of unconsciousness and insensibility of the salmon was provided on the electroencephalogram (EEG) by the appearance of slow waves and spikes, followed by a strong depression in electrical activity. This phenomenon was observed in 17 salmon after percussive stunning using an air pressure of 8.1 to 10 bars, whilst 8 fish were considered conscious at pressures below 8.1 bars although some were seemingly unconscious on behaviour. Consequences were a haemorrhage in the brain cavity in 15 out of 17 fish, broken upper or lower jaws in 9 fish and eye burst in 8 fish. A general epileptiform insult (unconscious and insensible) was obtained by delivering a voltage, consisting of a direct current (DC) coupled with 100 Hz alternating current (AC) with a peak value of approximate to 112 volt (V), head to body, for approximate to 0.5 s. The total duration of the insult was 62 +/- 44 s (mean +/- SD; n = 25) which was followed by minimal brain activity in 19 fish. The heart rate was 20 +/- 7 beats/min prior to stunning. After stunning the electrocardiogram (ECG) revealed fibrillation for 22 15 s and became irregular and showed extra systolae (ventrical contraction) afterwards. Exposing the salmon for 5 s with electricity followed by a gill cut resulted that 1 out of 3 fish recovered temporary after 3 min. Haemorrhages were not observed in the fillets. Average current for head to body electrical dry stunning was 668 milliampere (mA) root mean square (RMS) with an average stunning voltage of 107.9 V-rms. Electrical head to body stunning can be recommended when using coupled AC and DC current of 668 mA(rms) and approximate to 107 V-rms. The salmon can be stunned in approximate to 0.5 s. However, a correct bleeding procedure should be developed. For percussive stunning we conclude that if sufficient force is used the fish will be rendered unconscious insensible which result in damage of the carcass, whereas a combined AC and DC can be recommended source for dry electrical head to body stunning. (C) 2009 Elsevier B.V. All rights reserved.