Amphibians, Fish, and Reptiles
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Euthanasia of ectothermic animals must take into account differences in their metabolism, respiration, and tolerance to cerebral hypoxia. In addition, it is often more difficult to ascertain when an animal is dead. Some unique aspects of euthanasia of amphibians, fishes, and reptiles have been described.[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]13,51,186,187[/FONT][/FONT]
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Injectable agents[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]—Sodium pentobarbital (60 to 100 mg/kg of body weight) can be administered intra-venously, intraabdominally, or intrapleuroperitoneally in most ectothermic animals, depending on anatomic features. Subcutaneous lymph spaces may also be used in frogs and toads. Time to effect may be variable, with death occurring in up to 30 minutes.[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]1,187,188 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Barbiturates other than pentobarbital can cause pain on injection.[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]189 [/FONT][/FONT]
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Clove oil[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]—Because adequate and appropriate clin-ical trials have not been performed on fish to evaluate its effects, use of clove oil is not acceptable. [/FONT][/FONT]
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]External or topical agents[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]—Tricaine methane sul-fonate ( TMS, MS-222) may be administered by various routes to euthanatize. For fish and amphibians, this chemical may be placed in water.[/FONT][/FONT]
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Inhalant agents[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]—Many reptiles and amphibians, including chelonians, are capable of holding their breath and converting to anaerobic metabolism, and can survive long periods of anoxia (up to 27 hours for some species).[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]197-202 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Because of this ability to tolerate anoxia, induction of anesthesia and time to loss of con-sciousness may be greatly prolonged when inhalants are used. Death in these species may not occur even after prolonged inhalant exposure.[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]203 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Lizards, snakes, and fish do not hold their breath to the same extent and can be euthanatized by use of inhalant agents. [/FONT][/FONT]
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Carbon dioxide[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]—Amphibians,[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]1 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]reptiles,[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]1 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]and fish[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]203-205 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]may be euthanatized with CO[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]2[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]. Loss of con-sciousness develops rapidly, but exposure times required for euthanasia are prolonged. This technique is more effective in active species and those with less tendency to hold their breath. [/FONT][/FONT]
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Physical methods[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]—Line drawings of the head of various amphibians and reptiles, with recommended locations for captive bolt or firearm penetration, are available.[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]13 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Crocodilians and other large reptiles can also be shot through the brain.[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]51 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Decapitation with heavy shears or a guillotine is effective for some species that have appropriate anatomic features. It has been assumed that stopping blood supply to the brain by decapitation causes rapid loss of consciousness. Because the central nervous sys-tem of reptiles, fish, and amphibians is tolerant to hypoxic and hypotensive conditions,[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]13 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]decapitation must be followed by pithing. [/FONT][/FONT]
[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]188 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Two-stage euthanasia procedures[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]—Propofol and ultrashort-acting barbiturates may be used for these species to produce rapid general anesthesia prior to final administration of euthanasia. In zoos and clinical settings, neuromuscular blocking agents are considered acceptable for restraint of reptiles if given immediately prior to administration of a euthanatizing agent.Most amphibians, fishes, and reptiles can be euthanatized by cranial concussion (stunning) followed by decapitation, pithing, or some other physical method. [/FONT]
[FONT=Times New Roman,Times New Roman]Severing the spinal cord behind the head by pithing is an effective method of killing some ectotherms. Death may not be immediate unless both the brain and spinal cord are pithed. For these animals, pithing of the spinal cord should be followed by decapitation and pithing of the brain or by another appropriate procedure. Pithing requires dexterity and skill and should only be done by trained personnel. The pithing site in frogs is the foramen magnum, and it is identified by a slight midline skin depression posterior to the eyes with the neck flexed.[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]187 [/FONT]
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[FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Cooling[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]—It has been suggested that, when using physical methods of euthanasia in ectothermic species, cooling to 4 C will decrease metabolism and facilitate handling, but there is no evidence that whole body cooling reduces pain or is clinically efficacious.[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]206 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Local cooling in frogs does reduce nociception, and this may be partly opioid mediated. [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]207 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Immobilization of reptiles by cooling is considered inappropriate and inhumane even if combined with other physical or chemical methods of euthanasia. Snakes and turtles, immobilized by cooling, have been killed by subsequent freezing. This method is not recommended.[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]13 [/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]Formation of ice crystals on the skin and in tissues of an animal may cause pain or distress. Quick freezing of deeply anesthetized animals is acceptable.[/FONT][/FONT][FONT=Times New Roman,Times New Roman][FONT=Times New Roman,Times New Roman]208 [/FONT][/FONT]