Electrical Stunning Q&A - Workshop by ASC and CAP | Centre for Aquaculture Progress

Are you planning an ASC improver programme dedicated to implementation of stunning machines in sea bass / sea bream farms?

ASC: Currently, there is no planned Aquaculture Improver Programme (AIP) for the models where we already have the AIP running in Asia. However, discussions are ongoing regarding new projects to support the implementation of farm standards, including topics related to stunning machines and small farmers. If such an initiative is confirmed, it would align with broader efforts to improve welfare practices in sea bass and sea bream farms. Would you like more details on the ongoing discussions or potential future directions? Follow up in a couple of months when I will have a clearer perspective on these programs.

For wet stunning, I understand that only sea water is used?

CAP: In relation to sea bream and sea bass: yes, seawater is used.

Scientific research shows there is no stat significant difference between electrically stunned/not stunned fish. Which parameters does this research look at?

CAP: The research looks at parameters including: overall sensory evaluation of cooked fillets, overall carcass quality, overall appearance, objective measurements of color, freshness indicator Ki values, quality index method scoring, and flesh pH 24 hours post-mortem.

When will the new ASC standard be made public?

ASC: The new ASC standard is expected to be made public very soon, in Q2 2025.

Please define the back up system for stunning that needs to be in place. Does a second electric stunner need to be presented during the ASC inspection audit? How will it be possible to stun the portion-size fish?

ASC: The main stunner is expected to be effective in stunning all fish sizes at the farm. In case of any ineffectiveness, corrective actions should be in place, such as manually stunning fish that were not effectively stunned using a manual stunner (e.g., a priest).

Regarding the backup system for stunning, it is important to define a reliable contingency plan. A backup system—such as an additional electric stunner or an alternative stunning method—can help ensure compliance with welfare standards. However, the farm may also choose to stop the harvest and manually stun the fish on the line until the issue is verified and resolved.

For portion-size fish, the stunning method should be adapted to ensure effectiveness, whether through adjustments to the main stunner settings or an alternative method.

For the new ASC Farm Standard, will ice slurry killing be permitted without prior electrical stunning for seabass/seabream?

ASC: No, killing is not permitted before stunning under the new ASC Farm Standard. This means that ice slurry killing without prior electrical stunning will not be allowed for seabass and seabream.

The requirement for stunning before killing is based on animal welfare principles, ensuring that fish are rendered unconscious and insensible to pain before any further processing. Stunning reduces stress and suffering, aligning with best practices in humane harvesting. The ASC standard emphasizes effective stunning methods to uphold these welfare standards and ensure ethical treatment of farmed fish.

How long should the fish stay stunned to avoid recovery before death?

CAP: The fish will need to stay stunned until death. If placed in ice slurry immediately after being stunned, the fish should remain unconscious, assuming it was stunned correctly.

Despite the fact that Asian countries in the Global South account for a significant share of global aquaculture fish production, why are most welfare certification bodies, research efforts, and stunning methodologies primarily developed for fish species in the Global North?

ASC: Strategic models were first developed for the most valuable species in the market, starting with salmon. However, welfare needs, flesh quality, and sustainability goals apply to all species. This is why the focus is now expanding southward, incorporating the same sustainability principles into other regions and species.

Despite the significant share of global aquaculture production in Asian countries, most welfare certification bodies, research efforts, and stunning methodologies have been primarily developed for fish species in the Global North due to several factors:

Market Demand & Economic Drivers – Higher-value species like salmon, predominantly farmed in the Global North, have driven early welfare and quality-focused innovations due to consumer demand for ethical and high-quality products.

Regulatory Frameworks – Countries in the Global North have historically implemented stricter animal welfare regulations, prompting research and certification development.

Technological Development – Advanced aquaculture industries in regions like Europe and North America have had more resources to invest in R&D for welfare improvements, including stunning technology.

Industry Structure – The industrialized, vertically integrated nature of aquaculture in the North facilitates easier adoption of standardized welfare measures compared to more fragmented, small-scale farms in parts of the Global South.However, as awareness grows, efforts are increasingly shifting to address species and farming systems in the Global South, ensuring welfare standards, sustainability, and ethical practices are globally applied.

Will there be similar seminars for other species?

ASC: For finfish, the same topic is not expected to be covered again, as the equipment structure and ASC requirements are similar across finfish species. However, other topics will be developed to address specific needs and advancements.

Are there any advantages / disadvantages when comparing dry and wet stunning?

CAP: Each type of stunner has its own advantages / disadvantages. Dry stunning machines tend to be cheaper, and can be used with the traditional brailing method. They may also be more suitable for smaller boats. Wet stunning machines can take up less deck space if they are installed below the boat, and the fish do not spend any time out of the water while conscious.

When is fish stunning considered successful to comply with the standard?

ASC: Fish stunning is considered successful under the ASC standard based on behavioural observations, as this is the only practical method available on farms. To comply with the standard, the fish must show clear signs of unconsciousness immediately after stunning, including:
- Loss of balance – Fish should not be able to right themselves.
- No rhythmic opercular (gill) movement – Breathing should cease or be significantly reduced.
- No response to stimuli – The fish should not react to handling, touch, or other external stimuli.
- Eye roll – The fish’s eyes should not track movement, indicating loss of brain function.

If any of these signs are not observed, corrective actions must be taken, such as applying a secondary stun to ensure the fish is fully unconscious before further processing.

Reach out

Centre for Aquaculture Progress (CAP)
- Engineering Expert - Implementation Support, Martin Wicke: martin@centreforaquacultureprogress.org

Aquaculture Stewardship Council (ASC)
- Standards Manager - Health and Welfare, Maria Castanheira: maria.castanheira@asc-aqua.org
- Producer Engagement Manager, Nicholas Grimshaw: nicholas.grimshaw@asc-aqua.org