Evaluation of head-only and head-to-tail electrical stunning of farmed eels (Anguilla anguilla , L.) for the development of a humane slaughter method

Abstract

The overall objective was to evaluate the suitability of electronarcosis as a stunning method for farmed eels. In the first experiment the minimum electrical current needed to induce a general epileptiform insult by head-only stunning was assessed. The individual eels (n = 40) with a live weight of 700–800 g were fixed in a specially designed re-strainer. The EEG (electroencephalogram) and ECG (electrocardiogram) recordings, observation of behaviour and responses to pain stimuli were used to assess unconsciousness, insensibility and cardiac function. The applied current of 150, 200 or 250 V, 50 Hz, AC was delivered via scissor-model stunning tongs for approximately 1 s. A general epileptiform insult was observed in 31 eels for which a successful EEG recording was obtained, using 255 ± 4 V, 545 ± 32 mA, for 1.2 ± 0.2 s. The general epileptiform insult as measured on the EEG was characterized by a tonic/clonic phase and an exhaustion phase. The behaviour showed one phase: tonic cramps alternated by clonic ones. The heart rate was 22 ± 8 beats min−1 (n = 23) prior to stunning. After stunning the ECG revealed fibrillation. In the second experiment the behaviour of seven individual eels able to move freely in water was observed after head-only stunning (250 V). Two phases were distinguished. Limited tonic and clonic cramps combined with backward swimming were followed by heavy clonic cramps combined with unco-ordinated movements such as jumping out of the water. A distinct exhaustion phase was not observed in all animals. In the third experiment a head-to-tail electrical method was examined in 15 eels for rendering the eels unconscious and insensitive prior to slaughter. They were stunned by applying 253 V for 3 s followed by 50 V for 5 min. In the fourth experiment nine eels were head-only stunned with 260 V for 1 s immediately followed by 50 V for 5 min applied from head to tail. Results obtained in these two experiments were similar. After stunning no brain activity and no responses to pain stimuli on the EEG were observed and the ECG showed ventricular extra systolae. It was observed that it might take 60 ± 25 min or longer for a complete recovery. It can be concluded that for effective electrical stunning of eels with a weight of 700–800 g an average current of 545 ± 32 mA (at approximate 250 V, 50 Hz AC) is needed. In this case, within a confidence level of 95% at least 91% of the eels are effectively stunned (n = 31). Therefore, it is recommended to increase the minimum current for an effective stun in practice to 600 mA. Further research is needed to determine the conditions to induce permanent unconsciousness and insensibility of the eels to protect the animals at slaughter.