Stunning of farmed African catfish (Clarias gariepinus) using a captive needle pistol; assessment of welfare aspects

摘要

The objective of this study was to assess whether high-pressure injection of air into the brain of African catfish (Clarias gariepinus) could render the animal unconscious and insensible immediately and permanently. In the study, 48 African catfish with a live weight of 900-1900 g were restrained and equipped with EEG and ECG electrodes and then stunned. The catfish were stunned mechanically using a captive needle pistol. The pressure to shoot the needle was 8 bar and that to inject the air was 3 bar for 1.5 s. The catfish behaviour was observed during and after stunning. tau and delta waves and spikes, which precede a stoppage in brain activity as measured on the EEG, were used as indices for the measurement of immediate induction of unconsciousness and insensibility In 23 of 42 fish, an isoelectric line was observed after an average of 13.4 s, while in the remaining fish the tau and delta waves and spikes remained on the EEG during the recording period. In all cases, the ECG showed an irregular heart rate with fibrillation and extra systolac. Moreover, the configuration showed ischaemia. Before the captive needle stunning, free-swimming fish (n = 7) explored the tank for an average of 21 +/- 12 s before lying down at the bottom. After stunning, they showed clonic uncoordinated swimming movements. The movements stopped after an average of 38 +/- 50 s. In another group (n = 7) that was stunned and subsequently placed in ice water, clonic cramps were observed in two out of seven animals. When taking into account the number of animals with a reliable EEG (n = 42) and using 95%, confidence intervals, it was concluded that at least 93% of the catfish were effectively stunned using a correctly positioned captive needle pistol. Furthermore, it is recommended to immobilize the stunned fish by chilling, as the post-stun clonic cramps may hinder gutting and filleting.