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This is a very interesting question and at the moment we have to say - uncertain. The response of warm water prawn and shrimp appear notably different from cold water decapod species (i.e. crabs, lobsters, langoustine etc) where electrical stunning (ES) appears more reliable (from EEG and behavioural responses).
Review shows that (for warm water species) both ES or use of Ice slurry (at 5 to -2.5 degrees C) lead to "stun" as established under EFSA criteria - namely demonstrates one or more of the following:
- Loss of evoked responses (ERs) like visual evoked response (VER), or other such as no response to touch, etc.
- Generalized tonic clonic seizures with high EEG fluctuations, indicating no central brain processes.
Prolonged period of total power to values < 10% of those pre stun (i.e. FFT (Fast Fourier transform, an indicator of total power content)
However, there are variables with both techniques seeing behavioural responses associated with pain - i.e. tail flick, VER response etc post "stun" - hence actual behavioural measures (of unconsciousness) are unreliable; and both can lead to visible damage to the animal (rostral carapace and eyes). In addition ES leads to higher lactate measures (as a proxy for stress) vs ice.
In the interest of EA truth seeking we need to investigate more to establish best technique (or indeed combination of techniques - ie ice and ES, or ice at lower temperatures) to satisfy EFSA criteria. Until that is established i agree that we should be careful in establishing a process that has yet to be validated consistently. We should follow the "precautionary principle" in the interim but with the opinion that we must be open to new evidence (i.e. is ice better)?
My last point would be that almost always we talk and base our decisions on scientific standards. However, we must also understand that the in field conditions and practicality also affect results, very often significantly. Hence, methodology must also consider the in-field operation from a practical, socioeconomic, cultural or even religious position when making a recommendation.
I’m actually in the middle of a literature review on this exact topic - electrical stunning in decapod crustaceans. There’s reasonable evidence from several species (e.g., Carcinus maenas (crabs), Homarus gammarus (lobsters), Nephrops norvegicus (lobsters), Paranephrops zealandicus (crayfish)) that correctly applied electrical stunning can abolish neural activity for several hours, which is generally taken to indicate insensibility (Neil et al., 2024; Neil et al., 2022; Albalat et al., 2022).
There are no published studies directly measuring neural responsiveness in shrimp after stunning. However, post-stun behavioural quiescence in shrimp looks very similar to the behaviours seen in those other species where neural shutdown has been demonstrated. This is why it’s generally inferred that the method would work for shrimp as well, though experimental validation is still needed and mapping out how to achieve that will be one of the aims of my review.
I see, thank you! Has relative CNS inactivity been validated as a proxy for insensibility? Like, do humans with recorded low CNS activity report having been insensible during that episode?
If the central nervous system has truly stopped functioning, that would imply insensibility. That’s why loss of all measurable brain activity is taken as a sign of unconsciousness in clinical contexts. In humans, episodes with reduced CNS activity (for example, during deep anaesthesia or certain brain injuries) are generally associated with a lack of subjective experience.
For decapods, the challenge is that most studies measure spontaneous CNS activity rather than testing every possible form of responsiveness, such as testing to see whether we can evoke CNS responses through stimulation. So while prolonged inactivity is a strong sign of insensibility, researchers should still gather more data to increase confidence (especially given that, as you mention, we are putting a lot of resources behind this!)
I see, thanks. Is it possible to measure spontaneous CNS activity from beginning to end of the stunning and asphyxiating process?
The studies I linked above started measuring 2-10 minutes after stunning, but there are other studies which have measured CNS activity before, during, and immediately after the stunning process - for example, Fregin & Bickmeyer (2016). Interestingly, they observed that before settling into a quiescent state, intense epileptic-form seizures occur in the CNS that last for up to an hour after stunning. In mammals, epileptic-form seizures are associated with a loss of consciousness and a lack of subjective experience during that period, suggesting insensibility (and this is roughly how the authors interpret their finding). However, more work needs to be done to better understand this phenomenon in decapod crustaceans.
I'm not focussing on the asphyxiation process, so I'll let someone with more knowledge in that area chime in. If no one does, I'd be happy to look into it!