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Head-only electrical stunning and bleeding of African catfish (Clarias gariepinus): assessment of loss of consciousness

Published online by Cambridge University Press:  11 January 2023

E Lambooij ,
RJ Kloosterboer ,
MA Gerritzen  and
JW van de Vis
E Lambooij*
Affiliation:
Animal Science Group, Wageningen UR, Division of Nutrition and Food, PO Box 6S, 8200 AB Lelystad, The Netherlands
RJ Kloosterboer
Affiliation:
Animal Science Group, Wageningen UR, Netherlands Institute for Fisheries Research (RIVO), PO Box 68, 1970 AB Ijmuiden, The Netherlands
MA Gerritzen
Affiliation:
Animal Science Group, Wageningen UR, Division of Nutrition and Food, PO Box 6S, 8200 AB Lelystad, The Netherlands
JW van de Vis
Affiliation:
Animal Science Group, Wageningen UR, Netherlands Institute for Fisheries Research (RIVO), PO Box 68, 1970 AB Ijmuiden, The Netherlands
*
* Correspondence: bert.lambooij@wur.nl
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Abstract

The objective was to evaluate the welfare implications of electrical stunning prior to gill-cutting of farmed African catfish as an alternative to live chilling in combination with gutting. Electroencephalogram (EEG) and electrocardiogram (ECG) recordings, in combination with observation of behaviour and responses to noxious stimuli, were used to assess brain and cardiac function in African catfish (body-weight 1571 ± 362 g [mean ± standard deviation], 32 males and 26 females). In the first experiment, the minimum electrical current required to induce a general epileptiform insult by head-only stunning was determined. The individual catfish were fixed in a specially designed restrainer, and applied voltages of 150 V, 200 V, 250 V, 300 V or 350 V (50 Hz AC) were delivered via scissor-model stunning tongs for approximately I s. A general epileptiform insult was observed in 31 fish, for which a successful EEG recording was obtained using 362 ± 32 V, 629 ± 180 mA for 1.2 s. The durations of the tonic, the clonic and the exhaustion phases were 8 ± 3 s, 12 ± 7 s and 7 ± 5 s as measured by EEG, respectively; a distinct exhaustion phase was not clear in II fish. The total duration of the insult was 23 ± 8 s. After the insult the fish recovered. The heart rate was 63 ± 29 beats min I prior to stunning. After stunning, the ECG revealed extrasystole and was irregular. By using an average current of 629 ± 180 mA (at approximately 360 V, 50 Hz AC), at least 91% of fish are effectively stunned with a confidence level of 95%. In the second experiment, the behaviour of 10 individual catfish, which were able to move freely in water, was observed following head-only stunning (370 V). The durations of the tonic, clonic and exhaustion phases in free-swimming fish were II ± 8 s, 20 ± 5 s and 23 ± 20 s, respectively. All fish recovered. In the third experiment, a group of seven catfish was head-only stunned followed by gill-cutting to kill them as a second procedure (ie after recovery from head-only stunning). No brain activity was seen on the EEG 12 ± 5 s after stunning. However, two fish showed responses to noxious stimuli after 2 min and 5 min. A second group of seven catfish was gill-cut only. They responded to noxious stimuli for at least 15 min. The blood loss was 1.2% and I.0% of live weight for the first and second group, respectively. It may be concluded from our results that African catfish are effectively stunned for 23 ± 8 s with a current of 629 ± 180 mA for 1.2 s, after which they recover. Since evoked responses may remain for at least 5 min after stunning and gill-cutting, we recommended that the stunning and killing procedure should be optimised.

Keywords

animal welfarecatfishClarias gariepinuskillingslaughterstunning
Type
Research Article
Information
Animal Welfare , Volume 13 , Issue 1 , February 2004 , pp. 71 - 76
Copyright
© 2004 Universities Federation for Animal Welfare

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