Electrical Stunning of Edible Crabs

Summary

In the project StunCrab, kindly supported by the Norwegian Research Council, SeaSide AS, Hitramat AS and Nofima has successfully developed and implemented electrical stunning of edible crab. The research has shown highest impedance for crabs in the region of 40-100 Hz, confirming 50 Hz as an adequate frequency. Crabs, however, have a high and size-dependent resistance. In order to stun the crab within 1 s, the direct exposure must be 220 V, 50 Hz AC, however, due to the high resistance, at least 10 s exposure is recommended. To ensure no revival the crab should be pre-chilled and kept in air or ice water after stunning. In a large scale test with 300 crabs placed in ice after stunning, no signs of conscience were observed before death. Percentage loss of extremities (claws or feet) was relatively independent of voltage or exposure time, and typically 3-6% loss at 220 V. Due to the high contact resistance measured, effect of current is lost rapidly. To ensure good contact, spraying of the crabs with salt water prior to stunning and use of a conveyor belt to avoid single contact point between electrodes and crab, is recommended. IR camera revealed local heating, in particular in contact points of electrode with extremities. It is therefore recommended usage of a minimum current exposure time, 20 s maximum, and 10 s being optimum in most cases.