Abstract

The largest aquatic salamander in the United States, the hellbender (Cryptobranchus alleganiensis) once ranged in streams throughout the Eastern United States and west to Tennessee and the Ozarks of Missouri. Considered a sentinel of water quality, it is currently threatened, endangered, or even extinct across much of its previous range. There has been recent effort by a number of zoological institutions, governmental, and non-governmental agencies to work with this species, both in the field and in collections, often with head-start programs to supplement numbers in the wild.

For over 18 years, the Saint Louis Zoo has been working with hellbenders, both the Ozark (C.a. bishopi) and Eastern subspecies (C.a. alleganiensis). To date nearly 10,000 hellbenders have formed part of the Saint Louis Zoo's collection and reintroduction efforts.

As expected with a species that has large egg clutches, some developmental abnormalities are seen periodically, including scoliosis, kinked tails, intestinal atresia, hind limb agenesis, cloacal deformities with tendency to prolapse, and absence of ocular development. Larval edema has been seen without a known etiology. Some affected individuals can be managed but often the deformities are appropriate indications for euthanasia.

Clinical techniques used in hellbenders are similar to those employed for most amphibians. Some modifications are made for their unusual anatomy and physiology, including a thick slime coat, transition from a branchial to pulmonary respiratory system, and large lateral skin folds.

Anesthesia is most commonly performed using MS-222 with a more gradual induction than in most fish species. Anesthetic concentration is adjusted based on life-stage, primarily with respect to the presence or absence of gills. Recoveries are also slower and are longer with lower water temperatures.

Endoparasitism is seen occasionally and is managed on a case by case basis. Quarantine and treatment of food items should be considered, as many hellbender food items are intermediate hosts for a variety of parasites. Wild-caught animals are primarily affected and at Saint Louis, dracunculid species have been isolated on rare occasions.

Leeches, again primarily seen on wild caught animals, can be a concern as they may be the vector of Trypanosoma cryptobranchi.¹ Targeted removal of leeches from the animals and heat treatment of the water systems has greatly reduced the presence of T. cryptobranchi in the collection.

Hellbenders are at least partially tolerant of infection with Batrachochytrium dendrobatidis. In Ozark hellbenders, there may be a relationship between the development of ulcerative pododermatitis and chytrid status. Strict biosecurity protocols and targeted treatments with antifungals or hear are used to manage the collection and prevent spread of the disease.

Gram-negative bacterial infections are seen periodically, including Aeromonas, Pseudomonas, Acinetobacter, Citrobacter, Enterobacter, and Escherichia coli. As with other amphibians, these infections are opportunistic, most often secondary to water quality issues or other stressors.

The most common non-infectious diseases seen in the collection are ulcerative pododermatitis and conspecific bite wounds. Sporadic cases of neoplasia, cloacal prolapses, herniations, and gastrointestinal obstructions are seen.

Acknowledgements

The authors wish to thank the animal health and hellbender husbandry staff for their hard work and dedication in caring for these animals. They also want to acknowledge Jeff Briggler, Ph.D., Resource Scientist with the Missouri Department of Conservation, Jeff Ettling, Ph.D., Curator of Herpetology and Director of the Ron Goellner Center for Hellbender Conservation, and Mark Wanner, Zoological Manager of Herpetology and Assistant Director of the Ron Goellner Center for Hellbender Conservation for their dedication in saving this species.

* Presenting author

Literature Cited

1.  Junge RE. 2012. Hellbender medicine. In: Miller RE, Fowler ME, eds. Fowler's Zoo and Wild Animal Medicine Current Therapy. vol 7. Saint Louis, MO: Saunders; 260–265.