Options for Humanely Immobilizing and Killing Crabs

Trials were conducted on the Australian giant crab Pseudocarcinus gigas (Lamarck) to evaluate methods to: paralyze by injection (so that no muscular response is observed); paralyze by bath; humanely kill for scientific purposes; and humanely kill for human consumption. Treatments tested were: freshwater bath, chilling, heating, prolonged exposure to air, hypercapnic seawater bath (carbon dioxide addition), 2-phenoxy ethanol bath, magnesium sulfate bath, benzocaine bath, MS 222 bath, chloroform bath, clove oil bath, AQUI-S-TM bath, xylazine-HCl by injection, and ketamine-HCl by injection.

Xylazine-HCl (16 or 22 mg/kg) and ketamine-HCl (0.025-0.1 mg/kg), administered by injection, appear to be the best techniques for paralyzing crabs for short periods. Where injection is impractical, crabs may be successfully paralyzed within 30 min by a bath treatment of clove oil (greater than or equal to 0.125 mL/L) or AQUI-S-TM (greater than or equal to 0.5mL/L). Chloroform (1.25 mL/L; 1.5 h) rind clove oil (greater than or equal to 0.125 mL/L; less than or equal to 60 min) baths appeared to kill crabs humanely and are useful options for scientific use; however, clove oil is preferred because chloroform poses a human health risk. Of the methods tested, only clove oil and AQUI-S-TM appear premising as treatments for the humane killing of crabs for human consumption.