Electrical and percussive stunning of the common carp (Cyprinus carpio L.): Neurological and behavioural assessment

The overall objective of the study was to evaluate electrical and percussive stunning methods under laboratory conditions in common carps. The electrical current needed to induce a general epileptiform insult was assessed in 13 carps. The insult was obtained by delivering a current of 0.24 ± 0.03 A (163 ± 1 V; 50 Hz, a.c.) to the head, via scissor-model stunning tongs for approximately 1 s. The duration of the tonic, the clonic and the exhaustion phases were 11 ± 4 s, 5 ± 3 s and 20 ± 14 s on the EEG, respectively. An actual clonic phase was observed in two fish. The total duration of the insult was 31 ± 14 s. The heart rate was 22 ± 12 beats/min prior to stunning while after stunning, the ECG revealed fibrillation for 18 ± 7 s and was irregular. The behaviour of 10 individual carp, which were allowed to move freely in water, was recorded following head-only stunning (164 V, 0.23 ± 0.6 A). The duration of the tonic phase was approximately 10 s and the fish started fin movements after 48 ± 8 s and resumed swimming after 121 ± 83 s. A general epileptiform insult could be induced in carps (n = 25) by passing an electrical current through fresh water using 0.14 ± 0.03 A/dm2 (113 ± 17 V; electrode distance 16 cm) for 1 s at a water conductivity of 200 μS/cm. Twenty three carps were rendered unconscious and insensible during electrical stunning in fresh water, using 0.73 ± 0.05 A/dm2 (411 ± 2 V; electrode distance 16 cm) for 5 s at a water conductivity of 330 μS/cm, followed by chilling in ice water. As a second stunning procedure, carps were stunned mechanically using a percussion pistol at a maximal velocity of 10.99 ± 0.88 J. Evidence of unconsciousness and insensibility of the carps was provided by the appearance of theta, delta waves and spikes on the EEG, which were proceeded by no brain activity. However, two carp responded after 0.5 min to administered pain stimuli and one carp after 3 min. It may be concluded from this study that common carp are effectively stunned in fresh water. The application of an electrical current of 0.73 A/dm2 (26 V/cm, 50 Hz, a.c., 330 μS/cm) to individual carps in a tank in combination with chilling in ice water is an effective procedure for slaughter. The mechanical method of percussion stunning did not provide assurance of effective stunning as not all carp were unconscious and insensible after its administration.