Pithing is an effective method of killing some poikilotherms, but death might not be immediate, unless both the brain and spinal cord are pithed, which is recommended. Pithing of only the spinal cord should be followed by decapitation or another appropriate procedure. The anatomic features of some species preclude this method. Pithing requires some dexterity and skill and should be conducted only by trained personnel.
Snakes and turtles have been killed by freezing after immobilization by cooling. However, the 1989 report of the Universities Federation for Animal Welfare and World Society for the Protection of Animals (UFAW/WSPA, 1989) does not recommend that method; formation of ice crystals on the skin and in tissues of an animal can cause pain or distress.
Sodium pentobarbital (60 mg/kg) or other barbiturates can be administered, depending on anatomic features, intravenously, intracardially, or into the abdominal or pleuroperitoneal cavity of most cold-blooded animals.
Tricaine methanesulfate (MS 222) can be administered by various routes to induce euthanasia. For aquatic animals, it can be placed in the water—an effective but expensive means of euthanasia that is not hazardous to personnel.
Snakes, lizards, turtles, frogs, and toads can be killed by overexposure to gaseous anesthetics, such as halothane or methoxyflurane, in a chamber or by mask. CO2 can be used for terrestrial animals.
For additional reading on this subject, refer to Amphibians: Guidelines for the Breeding, Care, and Management of Laboratory Animals (NRC, 1974), The Relief of Pain in Cold-Blooded Vertebrates (Arena and Richardson, 1990), and Anesthesia in Fish (Brown, 1988).