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 unconsciousness must be long enough to allow killing without recovery. The objective of this study was to determine the stunner settings for effective tail-first dry electrical stunning of turbot (Scophthalmus maximus) and common sole (Solea solea). The fish were separated in two batches (B1 and B2). The turbot and sole in B1 were subjected to a short tail-first stun lasting for 1s and after 1min of recovery to a second, longer (20s) stun. The fish in B2 were exposed to a single long (20s) stun, which was tail-first in sole, but head-first in turbot. The short stun was applied to verify that the loss of consciousness was instant (i.e. within 1s), 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±0.91Arms by applying 125.5±0.6 Vrms (100Hz) in turbot and 1.22±0.68 Arms by applying 152.4±0.5Vrms in sole for 1s, 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 1s, followed by 1.44±0.41 Arms for 19s, 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 1s and 0.65±0.21 Arms for 19s 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 1s+0.35±0.22 Arms for 19s, and 1.20±0.59 Arms for 1s+0.36±0.15 Arms for 19s, 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. Statement of relevance The paper expedites stunning of turbot and sole in practice. •Tail-first dry electrical stunning followed by immersion in ice water was studied as a slaughter procedure for turbot and common sole•Applied stunner settings rendered most fish unconscious instantly•Tail-first electrical stunning can be developed into an alternative