Stunning and killing of edible crabs (Cancer pagurus)
The stunning and killing efficiency of ice, superchilling (N2 gas), freezing (–37°C), gradual heating (40°C), boiling, piercing of ganglia, salt baths (NaCl and KCl), gas (CO2) and electricity (50 Hz AC) on edible crabs was studied. Results showed
that electricity was the most efficient stunning method, whereby edible crabs could be rendered insensible within 1 s using electric field strengths of 400 V m–1 and above. Prolonging the electrical current to 10 s resulted in less potential difference (220 V m–1)
required to stun the crabs. Applying a two-stage stun with 530 V m–1 for 1 s followed by 170 V m–1 for 2 min resulted in a state of prolonged unconsciousness and 60% mortality. Failure to stun the crabs with electricity resulted in massive autotomy, where
all appendages were lost. Behavioural responses were lost in approximately 30% of crabs after 100 min of chilling on ice, while freezing did not render the crabs unconscious until temperatures of subzero were reached. The exposed chelipeds stiffened, and once frozen, irreversible damage was
caused. Placing crabs into heated seawater (40°C) led all responses to be lost after 5 min, while the internal temperature exceeded an average of 26°C, representing approximately 2.5 min of boiling. Gas, in the form of CO2, NaCl, and a low concentration of KCl (5%), failed
to render the animals insensible within 12 min. Using 20% KCl saw all animals lose all behavioural responses within 3 min. The piercing of single ganglions failed to kill the animal; both ganglia must be pierced in order to kill the animal. We conclude that electrical stunning is recommended
prior to boiling or carving, while piercing can alternatively be carried out by trained personnel.