It is not only inhumane to stab, drown or boil a crayfish, it is actually against the law.

In the latest edition of Biosecurity Magazine, the Ministry of Agriculture and Forestry has issued a timely reminder on the kindest way to despatch seafood delicacies such as crayfish and crabs.

"I think it's good to get the message out there, people still boil them which is just ugly," said ministry policy adviser on animal welfare, Joanna Tuckwell.

"I have never tried to kill [a crayfish] but I suspect they are not that easy to kill."

Popping live crayfish or crabs into a pot of boiling water was "inappropriate" because the animal's nervous system was still functioning on immersion.

It was also cruel to try to kill them with a blow to the head or other part of the body because they did not have a central nervous system.

"They have a spread-out nervous system, not a single one running down the spine," Ms Tuckwell said.

Drowning in fresh water was also inappropriate and caused "severe osmotic stress" (relating to the passage of liquids of different salt concentrations through a membrane).

The only humane way to kill a crayfish or crab was to chill it at between 2C and 4C until it was "insensible" and safely immobile.

It could then be killed with a sharp instrument either by head spiking (between the eyes) or chest spiking (through the chest wall from the underside).

Ms Tuckwell said the international debate continued on whether fish felt pain.

"It seems they do feel pain because they react quite quickly to negative circumstances," she said.

However, if you stabbed or boiled a live crayfish, it was unlikely you would be prosecuted under the Animal Welfare Act, even though crayfish are classed as animals under the act and it is an offence to kill an animal in a way which causes it "unreasonable or unnecessary pain or distress".

"We wouldn't be prosecuting people because we have other priorities," Ms Tuckwell said.