Assessment of electrical stunning in fresh water of African Catfish (Clarias gariepinus) and chilling in ice water for loss of consciousness and sensibility

The overall objective of the study was to evaluate loss of consciousness and sensibility after electrical stunning in fresh water and live chilling in ice water for slaughter of African catfish using measurement of electrical brain and heart activity. To provoke immediate loss of consciousness and insensibility, the minimum electrical current needed to induce a general epileptiform insult was assessed by placing a fish one by one in a tank between 2 plate electrodes in fresh water. The general epileptiform insult on the EEG (electroencephalogram) was characterised by a tonic, clonic and an exhaustion phase. After stunning, the ECG (electrocardiogram) revealed fibrillation. Within a confidence level of 95%, taking into account the number of animals with a reliable EEG (n = 24), at least 88% of all catfish are effectively stunned in fresh water by an average current of 1.60 ± 0.11 A/dm2 (50 Hz, sinusoidal, a.c.) at a conductivity of 876 ¿S of the water. After electrical stunning in combination with decapitation the fishes showed minimal brain activity until death by bleeding. For assessment of live chilling, 28 individual catfish kept in aerated tap water of 24 °C were placed one by one in ice water of 0.1 ± 0.5 °C for 30 min. The fishes showed swimming followed by clonic muscle cramps and became motionless at the end. No response on pain stimuli on the EEG appeared after a median of 12.5 min (5 to 20 min) at a body temperature of 13.7 ± 2.6 °C (n = 22). When taking into account the number of animals with a reliable EEG (n = 22) and using 95% confidence intervals, it was concluded that at least 87% of the catfish were unconscious and insensible at a decrease in body temperature of approximately 8.7 °C. Live chilling of African catfish resulted in an extremely high heart rate (tachycardia). Values between 294 ± 47 and 311 ± 38 beats/min (n = 13) were measured, where a normal value is between 70 and 80 beats/min. It was observed that unconscious and insensibility can be induced instantaneously by electrical stunning in fresh water. To kill the fish for slaughter decapitation is an option. Live chilling appeared to be a slow method. Whilst the African catfish was still conscious and sensible muscle cramps and tachycardia both occurred which may indicate stress