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Signal crayfish are an invasive species in the UK. They are also really tasty and catching them can be a fun picnic activity for adults and children. A recent study has found that they, along with all decapod crustaceans, appear to be sentient and should be protected from unnecessary suffering:

There is also substantial evidence of sentience in astacid lobsters/crayfish (infraorder Astacidea). We have either high or very high confidence that these animals satisfy criteria 1, 2 and 4.

They have some recommendations, that appear aimed at professional catering establishments:

Slaughter (decapods). We recommend that the following slaughter methods are banned in all cases in which a more humane slaughter method is available, unless preceded by effective electrical stunning: boiling alive, slowly raising the temperature of water, tailing (separation of the abdomen from the thorax, or separation of the head from the thorax), any other form of live dismemberment, and freshwater immersion (osmotic shock). On current evidence, the most reasonable slaughter methods are double spiking (crabs), whole-body splitting (lobsters), and electrocution using a specialist device on a setting that is designed and validated to kill the animal quickly after initially stunning it.

I have searched for whole-body splitting (lobsters), but only get instructions relating to cooked lobsters. It also seems that doing so prior to boiling exposes the flesh to much more of the water as well as releasing intestinal contents, which would be expected to impair their flavor. I am somewhat familiar with working with electricity, and I could probably rig up something to expose them to mains AC, but it sounds tremendously dangerous to attempt. For reference the ones we tend to get are in the range 2 - 4 inches long.

What is the best way to kill and cook signal crayfish in a way that is consistent with humane animal welfare?

I note this question, but it is specifically about lobster, the greater size of which would make splitting easier and also the answers recommend methods that are advised against in the recent paper such as freezing (which in a domestic freezer could well be worse than boiling).

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    Care for them and feed them. In approximately 3-8 years they'll die in the most humane way possible.
    – Richard
    Nov 24 '21 at 14:43
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    A cooking forum is not really the place to debate whether certain methods will or will not cause suffering to an innocent animal, not to mention discussing areas of animal welfare, high / low order brain functions and philosophical definitions of what constitutes pain. We cannot truly know if methods like putting them in the freezer or clove oil really do not cause pain unless we experience from the point of view of the animal itself, so we just settle on methods that are "good enough" based on our best guess and societal / cultural norms. How about we just stop exploiting animals instead?
    – F Chopin
    Nov 24 '21 at 15:15
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    I think a question on food ethics may be better suited to the philosophy SE or the vegetarian SE. We have a vegan site here if you were unaware.
    – Neil Meyer
    Nov 24 '21 at 18:20
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    Glib answer: "don't eat them".
    – Steve
    Nov 24 '21 at 21:08
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    Boiling them alive may well be illegal in the UK soon.
    – Dave
    Nov 25 '21 at 8:33
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Food tech. guru Dave Arnold experimented with crustacean killing...mainly lobster, and mainly in search of quality. He wound up with the use of anesthesia as the best method...and probably most humane. He uses clove oil to do the job. It was done years ago, but you can read his entire post here. He adds 10ml of clove oil to 90ml of ethanol. He places lobsters in salt water (sea water is best, otherwise approximate ocean salinity). Then add about 2ml of anesthesia per gallon. Read the post. It is quite detailed and offers other options for fish and seafood slaughter.

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    This is interesting, and I had missed it in the report. They say "these pharmacological studies typically use behavioural indicators of stunning, which do not distinguish anaesthesia from paralysis. Eugenol’s mode of action is also poorly understood. Whilst pharmacological anaesthetics are potentially effective, more research is needed." Possibly the best available.
    – Dave
    Nov 23 '21 at 17:40
  • If you want to be extra careful, you could combine clove oil with an ice slurry, and be pretty much certain that the mudbugs are comatose.
    – FuzzyChef
    Nov 23 '21 at 17:41
  • I wouldn't want to eat anything with clove oil in it. It is nasty. A tiny drop on sensitive skin is very painful. Nov 25 '21 at 9:23
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    This is an interesting, if complicated approach but the article you link is only concerned with taste, not with humane killing. To wit, clove oil is toxic, but it’s not a proved anaesthetic. — To quote Wikipedia: “there is insufficient medical evidence to support [its use as an analgesic].” While it’s possible (maybe plausible?) that it does in fact anaesthetise crustaceans, it’s just as possible that what it really does is simply paralyse them, and they still die painfully. We simply know too little about pain reception in crustaceans to tell. There’s a lot of pseudoscience in kitchens. Nov 25 '21 at 10:08
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Timely question!

As you've ascertained, any form of head-splitting with a knife -- as you would for crabs or lobsters -- is impractical for crayfish, simply because they are too small.

Putting together several sources, the recommended method is: after purging and picking out the dead ones, place the crayfish in a freezer or in an ice slurry, until the crayfish are reduced to between 2-4C. They will be dormant and unconscious at that point, and can be thrown into a large pot of vigorously boiling water where they will theoretically die before really waking up.

Spiking their heads unfortunately does not work with crayfish due to their distributed nervous system structure. The only other method the RSPCA recommends is electrical shock, which is impractical for home cooks.

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    The linked report is very scathing of chilling as a humane method, see section "Exposure to inappropriate temperatures."
    – Dave
    Nov 23 '21 at 17:43
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    Not seeing that section? I'm going of this ASPCA quote: "Scientific proof of the association between chilling and absence of discomfort, stress or pain is limited. However, this process is commonly considered to be effective, as crustaceans subjected to chilling do not show the behavioural signs of stress that occur when some other killing methods (such as boiling) are used. [12] "
    – FuzzyChef
    Nov 23 '21 at 17:51
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    Start of page 68, and also Slaughter (dispatch) using extreme temperatures (page 74). They basically say you cannot distinguish between anesthesia and incapacitation, and there are signs of distress: "Edible crabs autotomise during freezing (Roth & Øines, 2010), and this may be considered a credible indicator of distress against a background of considerable evidence of sentience (see Part III). This prolonged suffering may be worse than fast methods considered inhumane (e.g. boiling)."
    – Dave
    Nov 23 '21 at 17:57
  • Also "The welfare issues outlined in the section on stunning also apply here: nervous system activity continues after chilling, melting slush-ice can cause osmotic shock, and death is slow"
    – Dave
    Nov 23 '21 at 17:59
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    Too bad they didn't test clove oil, at all.
    – FuzzyChef
    Nov 23 '21 at 18:03

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