I would go with chilling. It is effective no matter the decapod's size, and it is probably the most humane way to euthanize them. I find that the effectivity of the clove oil is size-dependent and taxon-dependent; it works better in smaller specimens, and in non semi-terrestrial taxa. Larger specimens with particular respiratory adaptations can take a really long time for the clove oil to be effective. Cheers

I put larger animals, including large beetles and other critters in boiling hot water. That will kill them almost instantly.

The unbloody method is anesthetize in 7% MgCl2. (50% freshwater and 50% seawater). They are relax in 10 or 15 minutes and then they fix in formalin or alcohol.

Dear Ton,

Yes, the boiling water is one of the possible ways, but I need to preserve crustaceans fresh and therefore this method is inapplicable for me.

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Dear Victoriano,

This method of anesthesia is new for me. Thank you very much for your suggestion. Is it usable for freshwater crustaceans only or for marine species as well?

I used it only with marine species. You need to test it with freshwater species

If you put them in the freezer for a while, that will work very well, they relax very quick and you can get them out before the tissue freezes. The other and quicker option is to mix 40% salt, 40% crushed ice and another 20% of water. This mixture goes well below 0C and you can dip them into the mixture, either as they are, or in plastic bags if the salt-water mixture would affect your subsequent treatments.

Good luck!

Put your crustacean speciments into cold water (marine or fresh water added with ice).

Dear all,

Thank you very much for your suggestions.

Do you have any experience with use of clove oil in this context?

No I dont have. Is that a good preservation?

One Czech taxidermist uses the clove oil to euthanasia of crayfish, not for preservation... But I just heard it and I have no my own experience.

The method of immersion in MgCl2 solution is generally not effective with large crabs or semi-terrestrial/terrestrial ones. With these, I had some success by injecting the solution into the body with a syringe and needle (e.g. through the soft epithelia where the legs articulate on the body). The immersion method may work better with crustaceans that have external gills.

If I had chilling available in the field, I would try it first.

Ok, thank you. The needle application looks more drastic than chilling in this regard... Is it?

And what about CO2? Is it usable for euthanasia of decapods similarly as in fish?

The most rapid way would probably be electricity. "Crustastun" is a machine developed to kill decapod crustaceans. As i understand, originally developed for chefs/Cooks, but i know some researcher have started using it and we have also considered getting one. http://www.crustastun.com/ . A bit more expensive (~£ 2500) than a freezer or MGCl2 solution but the animal is dead in seconds.  

For research purposes there are several good ways to kill a decapod. Ice or chilling to make them torpid works really well except on cold-adapted species. Clove oil is used for some crustaceans and it works well as an anaesthetic. I wouldn't use it on a large scale. Injection of supersaturated KCl into the ventral nerve ganglion is used to kill lobsters. The method was published by Battison et al. several years ago. I use it regularly when I'm not examining hemolymph ions. I haven't used the crustastun method as ice works well for most of my applications. Magnesium chloride is an irritant to decapods and will result in them autotomizing legs. I don't recommend it. The same goes for weak solutions of ethanol.

Dear Jeffrey,

Thank you very much for your explanation.

Back to the clove oil (and eugenol). Which concentration is recommended? According to recent papers (e.g. Parodi et al., 2012), it seems that decapod species have specific sensitivity to this oil. Or certain concentration, which can be generalized over the Decapoda order including freshwater species, is known?

I would go with chilling. It is effective no matter the decapod's size, and it is probably the most humane way to euthanize them. I find that the effectivity of the clove oil is size-dependent and taxon-dependent; it works better in smaller specimens, and in non semi-terrestrial taxa. Larger specimens with particular respiratory adaptations can take a really long time for the clove oil to be effective. Cheers

I have one more question - is there a reflex whose absence can signal the death in decapods like as ocular reflex in fish?

Yes. By mechanic stimulation (using spatula for example) you can touch the eye stalk. absence of rezpone

Sory. (continue) Absence of the eye stalk response indicates the animal is death.

I have found that the use of reflex response in larger decapods is not a good indicator of death. The absence of response can result from morbidity due to disease, too, and some animals may look dead, but their hearts are still beating, so it depends on the question your addressing. However, for all intents and purposes, the animal is torpid and thus can be examined accordingly. You can touch the eyestalk, look for limb responses to stimulus, antennal responses, movement of mouthparts, etc., too as indicated by Bambang Irawan. Javier Luque's comments on clove oil are spot on. It works well for small crustaceans, but use ice for larger ones. I used a -20C room to anesthetize tropical species and it took around 20-30 minutes for them to stun and 45-60 minutes for death.

Ok, thank you for your responses.