Effectiveness of tail-first dry electrical stunning, followed by immersion in ice water as a slaughter (killing) procedure for turbot (Scophthalmus maximus) and common sole (Solea solea)

To protect the welfare of fish at slaughter, these animals should be rendered unconscious and insensible prior to killing. Furthermore, the state of unconsciousnessmust be long enough to allowkillingwithout recovery. The objective of this study was to determine the stunner settings for effective tail-first dry electrical stunning of turbot (Scophthalmusmaximus) and common sole (Solea solea). The fish were separated in two batches (B1 and B2). The turbot and sole in B1were subjected to a short tail-first stun lasting for 1 s and after 1 min of recovery to a second, longer (20 s) stun. The fish in B2were exposed to a single long (20 s) stun, whichwas tail-first in sole, but headfirst in turbot. The short stun was applied to verify that the loss of consciousness was instant (i.e. within 1 s), whereas the long stun (followed by immersion in ice water) was performed with the aim of showing that it is feasible to kill the fish without recovery. Loss of consciousness and sensibility were assessed using electrophysiological (EEG and ECG) and behavioural parameters. After administering a current of 2.39 ± 0.91 Arms by applying 125.5 ± 0.6 Vrms (100 Hz) in turbot and 1.22 ± 0.68 Arms by applying 152.4 ± 0.5 Vrms in sole for 1 s, 25 out of 26 turbot and 9 out of 10 sole in B1 exhibited EEG patterns showing that the fish were rendered unconscious instantly. The long tail-first exposure of turbot in B1 to 3.88 ± 1.26 Arms for 1 s, followed by 1.44 ± 0.41 Arms for 19 s, followed by immersion in ice water, led to an irrecoverable stun in 21 out of 22 fish, whereas the long head-first stunning of turbot in B2 (n = 13) resulted in passing 1.27 ± 0.40 Arms for 1 s and 0.65 ± 0.21 Arms for 19 s through the fish and no recovery during chilling. After the long, tail-first exposure of sole in B1 (n = 9) and B2 (n = 22) to 1.18± 0.49 Arms for 1 s+0.35 ± 0.22 Arms for 19 s, and 1.20± 0.59 Arms for 1 s + 0.36 ± 0.15 Arms for 19 s, respectively, none of the fish regained consciousness during the chilling. We conclude that the tail-first electrical stunning, followed by immersion in ice water can be developed into an effective stunning and killing method for turbot and sole.