There has been much discussion as to how long the animals should be kept in the ice slurry before boiling or cutting up and whether the formation of ice crystals can cause pain. An opinion among scientists is that the smaller shellfish will die in a matter of seconds when dropped into boiling water. It is questionable whether a few seconds of possibly extreme pain is acceptable, and piercing the animals needs considerable skill.
Some work has been done by the late zoologist Dr John Baker into passing an electric current through a water tank, so stunning the animals, but this has only been researched on lobster and crab.
What is certain is that most invertebrates have sensory receptors. They respond to noxious stimulation such as pinching, squeezing or cutting of the body wall, and research has shown that there is a strong possibility they are susceptible to pain and stress. Lobsters dropped into boiling water have been known to show powerful struggling movements for up to two minutes, and Dr Baker concluded that these were indications of pain.
Very little is understood about invertebrates. What is certain, however, is that there will never be a truly humane method of killing these essentially healthy animals, and the advice of Shellfish Network is to leave them in peace.