Reviewing euthanasia protocols for exotics

By Olivia A. Petritz, DVM, DACZM

Euthanasia should minimize or eliminate pain, anxiety, and distress through rapid loss of consciousness, followed by cardiac and respiratory arrest, and ultimately loss of brain function. The latter is challenging to assess in most animals, including zoological companion animals. Death occurs through direct depression of the central nervous system (CNS), hypoxia, and physical disruption of brain activity. Exotic pets, such as birds, reptiles, and fish, pose more unique challenges than domestic dogs and cats. How do you tell if a fish is painful? What about a snake or a bird? How do you tell if an animal with significant breath-holding abilities (such as an aquatic turtle) experiences true respiratory arrest? How do you euthanize an extremely small or extremely large animal? This article reviews euthanasia techniques for fish, reptiles, birds, and small mammals in a hospital setting.

A good reference for euthanasia of any species is the AVMA Guidelines for the Euthanasia of Animals,¹ which are available for free online, and were most recently updated in 2020. These guidelines describe acceptable, acceptable with conditions, and non-acceptable methods of euthanasia across multiple taxa.

Fish

According to the American Veterinary Medical Association (AVMA) guidelines, hypothermia and anoxia (desiccation after removal from water) are both unacceptable for fish euthanasia. The heart of a fish can continue to beat after brain death or removal from the body (up to four hours in decapitated goldfish). Therefore, the presence of a heartbeat is not a reliable indicator of "life" nor indicative of brain activity in fish. There are several recent publications on fish euthanasia techniques, including one by Balko et al.,² which found prolonged emersion in buffered MS-222 (Tricaine methanesulfonate) alone was inadequate for euthanasia of goldfish, a hypoxia-tolerant species. In that study, immersion in 1,000 mg/L (5-10 times the anesthetic dose) of buffered MS-222 resulted in death of only seven percent of immersed adult goldfish.

Another study³ found slightly different results, in that a high dose (1000 mg/L) of buffered MS-222 was efficient to euthanize juvenile goldfish. The  same authors also evaluated using continuous topical delivery over the gills of both MS-222 or clove oil for euthanasia of juvenile red head Tapajos eartheaters (Geophagus pyrocephalus) compared with prolonged bath submersion with either of those drugs.⁴ Interestingly, the immersion bath yielded a statistically faster mean time to cardiac arrest compared with continuous topical delivery routes. Regardless, a two-step process is still recommended for companion fish (Figure 1).

Reptiles

Challenges with reptile euthanasia include increased resistance to hypoxia, difficult vascular access, and slow metabolism. Therefore, euthanasia may take hours in certain reptile species. It is also important to remember the presence of a heartbeat does not equate to "life," as the heart can continue to beat in many reptile species even after the heart has been removed from the body and placed in formalin.

Unfortunately, electroencephalograms (EEGs) are not widely available for reptile patients, nor are there published normal values in any reptile species to date. The presence of a heartbeat is best determined using Doppler ultrasound or standard ultrasound, as stethoscopes are challenging to use in most reptiles due to scaled skin and the carapace and plastron in chelonians (Figure 2). It is recommended to listen for a heartbeat via Doppler for at least one to two minutes due to slow heart rates across most reptilian species, especially if heavily sedated.

In this author's clinical experience, an intravenous or intracardiac injection of KCl following pentobarbital administration in an unconscious reptile significantly hastens cardiac arrest.

Acceptable AVMA-approved methods of euthanasia include injectable agents (IV preferred, intracardiac if unresponsive to stimuli) or intracoelomic routes. Acceptable methods with conditions according to AVMA guidelines include inhalant anesthetics for certain species (snakes, some lizards). Many reptiles are capable of prolonged breath holding, intracardiac shunting, and are extremely hypoxemia-tolerant, which significantly reduces efficacy of both anesthesia and euthanasia via inhalant anesthetics as a sole method. Euthanasia via hypothermia alone is considered unacceptable under current AVMA guidelines.

A published study evaluated two routes of euthanasia administration as well as the efficacy of several drugs for euthanasia in a group of adult leopard geckos.⁶ All geckos were sedated with alfaxalone (20 mg/kg IM) and then divided into several euthanasia groups, including intracoelomic pentobarbital (400 and 800 mg/kg), intracardiac pentobarbital (800 mg/kg), intracardiac KCl (10 mEq/kg), and intracardiac lidocaine (100 mg/kg). Time to cardiac arrest for the intracardiac route for all three drugs was instantaneous. Cardiac arrest took 30-35 minutes for the intracoelomic route, which is clinically significant.

However, several undesirable effects were noted in this study. Multiple animals in the intracoelomic group had erythema at the injection site and an intermittent arched posture prior to cardiac arrest. Six out of nine geckos that received intracardiac KCl had severe muscle spasms, to the extent they were able to right themselves from dorsal to sternal recumbency post-cardiac arrest.  Most unexpected, six out of nine animals that received intracardiac lidocaine had spontaneous return of respiration and heartbeat five to six hours after initial cardiac arrest.  Therefore, intracardiac lidocaine and KCl are not recommended for euthanasia at these doses in this species.

There are several newer studies evaluating the efficacy of oral and cloacal transmucosal routes for euthanasia solution administration in reptiles with variable results. Oral and cloacal transmucosal administration of pentobarbital (100 mg/kg) was evaluated in red eared sliders.⁷ Seventy-five percent of turtles in the cloacal group had significant leakage of euthanasia solution, which required a rescue intravenous injection of pentobarbital. Respiratory arrest occurred in approximately 15 minutes, and cardiac arrest took significantly longer, with an average of 18 hours (range of six to 26 hours). The oral route was recommended, and while it was successful, cardiac arrest was prolonged. Oral transmucosal euthanasia was also evaluated in bearded dragons, and a two-dose protocol was used.⁸ Pentobarbital and phenytoin (100 mg/kg PO) was administered, and then a second dose (400 mg/kg) was administered orally 20 minutes later.

Leakage of euthanasia solution was also noted in this study, in addition to four lizards showing abnormal behaviors after the first dose, which could be secondary to pain. Time to cardiac arrest took an average of six hours. Transmucosal pentobarbital and phenytoin have also been evaluated in feral green iguanas at doses of 100 and 200 mg/kg.⁹ Rescue intravenous doses of euthanasia solution were needed for all iguanas administered euthanasia solution at both of these doses.

Birds

The avian section of the AVMA euthanasia guidelines refers to pet, aviary, falconry, racing, research, and zoo birds. Poultry are listed under a separate section, as there are some additional approved methods for that taxon. Acceptable methods for non-poultry birds include IV injection of a barbiturate in an unconscious or conscious bird. The AVMA guidelines specifically state an intravenous injection in a conscious bird cannot cause fear or distress; therefore, deep sedation or general anesthesia is highly recommended prior to euthanasia solution administration in any pet bird. The three most common veins utilized for this purpose include the right jugular, medial metatarsal, and ulnar veins.

In smaller birds, the jugular vein is likely the only one large enough for an intravenous injection. Placement of an intravenous catheter, for euthanasia or otherwise, is challenging in small birds and almost always requires heavy sedation or general anesthesia.

Therefore, intravenous injections are typically administered directly into the vessel rather than through an intravenous catheter.

If an intravenous injection is not possible, intracardiac, intracoelomic, or intraosseous routes of barbiturate administration could be considered. However, injections of euthanasia solution must avoid air sacs and pneumatized bones (femur, humerus, and others).

In addition, these routes are only considered acceptable in anesthetized or unconscious birds. Thoracic compression in a conscious bird is an unacceptable method of euthanasia according to the AVMA guidelines. There are two studies evaluating the efficacy of oral transmucosal routes of euthanasia in several wild bird species¹⁰ and in chickens,¹¹ with varying results.

Small mammals

Euthanasia techniques of small mammals (ferrets, rabbits, and rodents) are very similar to those of dogs and cats. Intraperitoneal injections are possible and AVMA-approved in many rodent species.

In the author's clinical experience, the time to cardiac arrest can be significantly delayed after intraperitoneal injections compared to intravenous or intracardiac injections. Rabbits and rodents are prey species; therefore, heavy sedation or general anesthesia is recommended prior to administration of euthanasia solution. Intravenous access can be challenging in many small mammals, especially if they are hemodynamically compromised. If intravenous access is not possible, an intracardiac injection could also be considered in an unconscious patient.

An intrarenal route for euthanasia of rabbits has also been recently described, and this is an AVMA acceptable method in unconscious animals.¹² The intravenous route was significantly faster for cardiac arrest than an intrarenal route, and 30 percent of rabbits needed a rescue IV dose of pentobarbital following intrarenal administration at the pentobarbital dosage evaluated (3 mL/rabbit).

Disposal of remains

Ideally, all small animals would be incinerated or cremated following euthanasia, but there are instances when an animal's remains are released to the owner for burial. Pentobarbital poses a serious risk of secondary intoxication to wildlife scavengers, including bald eagles.¹³ Burial regulations vary widely, and there are many different regional-specific laws regarding carcass burial. Clients should be educated about proper disposal and risks for secondary intoxication, ideally on a signed euthanasia consent form.

Olivia A. Petritz, DVM, DACZM, graduated from Purdue University and then completed several internships and a residency in the field of zoo and exotic animal medicine at the University of California, Davis. Dr. Petritz became a diplomate in the American College of Zoological Medicine in 2013, specializing in zoological companion animals (exotic pets). Petritz started an exotics service at a specialty hospital in Los Angeles, Calif., following her residency, and is currently an associate professor of Avian and Exotic Animal Medicine at North Carolina State University.

References

1. American Veterinary Medical Association (AVMA). (2020). AVMA guidelines for the euthanasia of animals: 2020 edition. Schaumburg, IL: AVMA.
2. Balko, Julie A., Ayako Oda, and Lysa P. Posner. "Use of tricaine methanesulfonate or propofol for immersion euthanasia of goldfish (Carassius auratus)." Journal of the American Veterinary Medical Association12 (2018): 1555-1561.
3. Perret-Thiry, Clément, Juliette Raulic, and Claire Vergneau-Grosset. "Evaluation of prolonged immersion in tricaine methanesulfonate for juvenile goldfish (Carassius auratus) euthanasia." Journal of the American Veterinary Medical Associationaop (2022): 1-5.
4. Leclerc, Lydie-Amy, et al. "EUTHANASIA BY CONTINUOUS TOPICAL DELIVERY OF CLOVE OIL OVER THE GILLS RESULTS IN DELAYED CARDIAC ARREST IN COMPARISON TO IMMERSION BATH IN JUVENILE RED HEAD TAPAJOS EARTHEATERS (GEOPHAGUS PYROCEPHALUS)." Journal of Zoo and Wildlife Medicine2 (2025): 303-310.
5. Heniff, Ashlyn C., and Julie A. Balko. "Potassium chloride administered via four routes for euthanasia of anesthetized goldfish (Carassius auratus)." Journal of Zoo and Wildlife Medicine3 (2023): 435-442.
6. Knutson, Kyra, et al. "Evaluation of Euthanasia Methods Using Injectable Agents in Leopard Geckos (Eublepharis macularius)." Journal of Herpetological Medicine and Surgery1 (2022): 35-41.
7. Ready, Zachary C., and Krista Keller. "Transmucosal pentobarbital is a successful euthanasia method in pond slider turtles (Trachemys scripta)." American journal of veterinary research7 (2023).
8. Wong, Amanda D., et al. "Transmucosal administration of pentobarbital and phenytoin solution induces euthanasia in bearded dragons (Pogona vitticeps)." American journal of veterinary research6 (2024).
9. Masri, Aiden, et al. "A Comparison of Intravenous and Oral Transmucosal Administration of Pentobarbital Sodium for Humane Euthanasia in White Leghorn Chickens (Gallus gallus domesticus)." Journal of Avian Medicine and Surgery3 (2025): 132-138.
10. Gardhouse, Sara, et al. "Evaluation of Oral Transmucosal Administration of Pentobarbital for Euthanasia of Conscious Wild Birds." Journal of Applied Animal Welfare Science (2021): 1-11.
11. Masri, Aiden, et al. "A Comparison of Intravenous and Oral Transmucosal Administration of Pentobarbital Sodium for Humane Euthanasia in White Leghorn Chickens (Gallus gallus domesticus)." Journal of Avian Medicine and Surgery3 (2025): 132-138.
12. LeGrand, Jessica L., et al. "Comparison of Intrarenal and Intravenous Injections of Sodium Pentobarbital for Euthanasia in New Zealand White Rabbits (Oryctolagus cuniculus)." Journal of the American Association for Laboratory Animal Science4 (2025): 770-777.
13. Viner, T. C., et al. "Integrating the forensic sciences in wildlife case investigations: a case report of pentobarbital and phenytoin toxicosis in a bald eagle (Haliaeetus leucocephalus)." Veterinary pathology5 (2016): 1103-1106.