Conditions for instant electrical stunning of farmed Atlantic cod after de-watering, maintenance of unconsciousness, effects of stress, and fillet quality — A comparison with AQUI-S™

Electrical stunning of farmed Atlantic cod is a method used to render the fish unconscious before further processing. However, evaluations of the stunning method at plants have shown that the electrical parameters need to be optimized to achieve instant stunning and prolonged duration of unconsciousness. One aim of the present study was to establish suitable stunning conditions for cod to comply with future fish welfare regulations. AQUI-S™ is an anaesthetic capable of producing rested fish at slaughter. In the current study, we wanted to assess some welfare aspects of using this agent. In addition, the two stunning methods were compared in terms of the magnitude of the stress response, and the resulting effect on product quality. The data show it was possible to stun cod instantly (0.5 s) at 107 Vrms, 0.5 + 0.2 Arms. However, it was necessary to expose the fish for a longer period (e.g. 15 s) to the same voltage to prolong the period of unconsciousness to facilitate killing without recovery. AQUI-S™ (68 mg L- 1) rendered the fish unconscious without recovery. No noticeable avoidance behaviour or distress was observed during stunning. Blood pH, lactate levels, and blood drainage, as determined after recovery, were similar for both stunning methods. The ability of the white muscle to twitch was not affected by treatment although electrical stunning caused a drop in initial white muscle pH. Hence, a tendency for a more rapid onset of rigor mortis was observed. No detrimental effects on product quality (Quality Index scores, tendency for gaping, ultimate pH, and fillet texture) were observed for either stunning method. Moreover, no blood spots and discolourations of fillets, or spinal fractures were observed. To comply with both good fish welfare protocols, and at the same time ensuring good product quality, we have fundamentally shown that this is indeed possible when cod are stunned with either of the methods described here