Review- Electrical Stunning Does Not Yet Ensure Prolonged Insensibility In Several European Finfish Species (Rethink Priorities)

We reviewed the evidence on electrical stunning for three small-sized European farmed fish species (~800M killed annually) to help interested stakeholders navigate uncertainty around the effectiveness of this technology in achieving humane outcomes.
For gilthead seabream and European seabass, electrical stunning is largely unproven. Further evidence is needed to demonstrate commercial stunners can deliver humane outcomes for these species even under optimal lab conditions.
The evidence is much more promising for small-sized rainbow trout. But results suggest performance is often variable and sensitive to machine calibration. More field studies would help confirm the technology works well in real-world conditions.
We recommend interested stakeholders help widen the evidence base, including through pushing machine manufacturers to make performance data more widely available and through facilitating field trials, ideally using innovative low-cost protocols where possible.

Around 800 million rainbow trout, gilthead seabream, and European seabass are farmed and killed annually for European markets.
Current slaughter methods for these species are widely considered inhumane, and electrical stunning might be the only viable option to stun these small-sized fish at scale.
Recognizing this, many major retailers, producers, and certifiers are seeking to transition towards electrical stunning for these species.
But the scientific evidence for whether electrical stunning actually achieves humane outcomes for these species is surprisingly sparse.

For gilthead seabream and European seabass, electrical stunning remains unproven.
- We found only a handful of lab studies for each of these species and no field trials.
- The higher-quality studies pointed to sensibility recovering within two minutes, much quicker than the 5–50 minutes that might be needed for follow-on slaughter processes to fully complete.
The evidence for rainbow trout is more promising, though variable and imperfect.
- We found 11 lab studies and one field trial for small-sized rainbow trout.
- Several high-quality lab studies pointed to machine settings associated with the majority of fish appearing insensible for at least 15 minutes, as did the field trial.

Major knowledge gaps remain: Electrical stunning seems very understudied for these species. We would feel more confident endorsing electrical stunning as a humane technology if the evidence base included field studies covering a wide range of machines and commercial settings.
Currently available electrical stunners plausibly offer counterfactual welfare improvements for rainbow trout, but the case is much weaker for seabream and seabass.

We recommend interested stakeholders help widen the evidence base for these species, including by pushing machine manufacturers to make performance data more widely available and by facilitating field trials.