Seabream (Sparus aurata ) is usually slaughtered by asphyxia on ice or ice-slurry, a method that does not immediately stun the fish and cause notable suffering. With the goal of finding a slaughter method that do not compromise the welfare of seabream, in this study we evaluated the welfare of adult seabream during the slaughter process using different stunning methods followed by one of two killing methods.
We stunned the fish with either electronarcosis as an alternative method for the industry, an anaesthetic (2-phenoxyethanol) as a control, or not applying any stunning as the current practice. Following stunning, we started a killing phase of either ice-slurry or ikejime, a Japanese technique consisting of impairing the brain of the fish with a sharp tool followed by exsanguination. We evaluated the welfare of the fish by using behavioural indicators such as the latency to lose opercular movement, eye-roll reflex, equilibrium, and swimming activity. We also implanted heart-rate bio-loggers that measured the heart rate activity and internal temperature of the fish as an additional method to evaluate fish welfare.
We found that electronarcosis stuns the fish immediately and 2-phenoxyethanol renders the fish unconscious within 100 s. No fish stunned with electronarcosis gained consciousness while they were in the ice-slurry, while only one fish stunned with anaesthesia gained consciousness after 18 min in ice-slurry. Ice-slurry did not stun the fish and the fish showed signs of distress within 55 s of being placed in ice-slurry and only losing consciousness within 15 min on average. Slaughtering with ice-slurry can take up to 40 min and it varies depending on the stunning method used and the individuals (Fig.1). Ikejime caused an immediate death, however performing the technique correctly required practice.
The bio-loggers showed that the internal temperature of the fish lowers at a very slow rate when exposed to ice-slurry, taking 24 minutes to go from 28 °C to 10 °C. The heart rate decreases over time, getting below 50 bpm within 2 min of exposure when no stunning method was applied beforehand, and increasing again after 23 min of exposure, showing some arrhythmias. Exposure to 2-phenoxyethanol reduced the heart rate from 90 to 70 bpm, and exposure to ice-slurry lowered it below 50 bpm within the first minute of exposure and maintained it low until the fish died. Electronarcosis lowered the heart rate from 83 to 65 bpm, and lowered it below 50 bpm within 1 min, also maintaining it low until the fish died.
Our results show that both anaesthesia with 2-phenoxyethanol and electronarcosis followed by ice-slurry are appropriate slaughtering method for seabream, and the slaughtering process can be even faster using the ikejime technique. Slaughtering only with ice-slurry induces suffering for 28 to 38 minutes and therefore should be avoided.