Biologic Data

The hellbender (Cryptobranchus alleganiesis) is a large aquatic salamander native to the United States. There are two subspecies; the eastern hellbender (C. alleganiensis alleganiensis) is found in the eastern United States from New York to Georgia, extending west through Tennessee and the Ohio River Valley to the Ozarks. The Ozark hellbender (C. alleganiensis bishopi) is restricted to the Ozark region of Missouri and Arkansas. Eastern hellbenders are larger (adults up to 70 cm length), with dorsal spotting, uniformly colored lower labium, and papillate elevations in the lateral line canals of the pectoral region. The Ozark subspecies is smaller (30 to 50 cm long) with a dorsal blotching pattern, mottled lower labium, and smooth-surfaced lateral line system in the pectoral region.¹⁵ Hellbenders have small lidless eyes, broad flat heads, and pronounced lateral skin folds. They produce a significant cutaneous mucous layer that is not toxic but may be irritating or noxious to mucous membranes (oral cavity). The hellbender is a habitat specialist dependent on appropriate temperature, dissolved oxygen, water flow, and substrate. They inhabit cold (5° C to 30° C), clear, swift-flowing streams with rocky bottoms. Large rocks must be present for nesting and refuge. Although lungs exist, respiration is almost entirely cutaneous. Hellbenders are long-lived (25 to 30 years and longer). Crayfish make up a large part of the diet, but also included are snails, nymphs, worms, tadpoles, and fish.¹² Hellbenders may be preyed on, especially larvae and juveniles, by fish, turtles, and water snakes, and were historically overharvested by humans for amphibian collectors. Currently, hellbenders are not a federally protected species, but such action is being considered.

Hellbenders are completely aquatic and mostly nocturnal, depending on range and habitat. Gills are present in larval stages, and adults have a singular pair of gill openings. Sexual maturity is reached at approximately 7 years of age. During breeding season (September through November), females often exhibit coelomic distension because of follicular development. Males develop a pericloacal swelling in breeding season, produced by enlargement of glands. Females may produce 300 to 450 eggs, and fertilization is external, unique among North American salamanders.¹⁵ Embryonic development is not precisely known because they have never reproduced in captivity; however, eggs collected in the wild have matured in captivity in approximately 30 days.

Hellbenders in the wild are threatened by stream impoundment, channelization, agricultural runoff (chemical and siltation), disturbances caused by recreational use, and thermal changes.²¹ As with amphibians worldwide, populations have declined dramatically in recent years; recent estimates of Ozark populations have suggested a 77% decline.²⁷

Captive Husbandry

Both subspecies of hellbenders are maintained in captivity. Attention must be given to water temperature, flow, and oxygenation, as well as providing an appropriate rocky substrate. Captive diets should mimic wild diets and include crayfish, earthworms, and fish. Routine weight monitoring is important because clinical signs of disease include inappetence, which may be difficult to determine unless regular weights are recorded. In addition, hellbenders have a normal seasonal weight fluctuation that should be monitored to differentiate it from health-related weight changes. Inadequate oxygenation of water may result in hellbenders surfacing frequently to breath or rocking in the water to increase circulation.

Infectious Diseases

Two infectious diseases, the fungus Batrachochytridium dendrobatidis and ranavirus infection, have been implicated as contributing factors of global amphibian declines.^5,7,18 There are no published reports of ranavirus prevalence in wild populations of hellbenders; however, ongoing research at the University of Tennessee, Knoxville Zoo, and University of Georgia has documented infection. In this study, ranavirus prevalence ranged from 25% to 65% in wild hellbender populations inhabiting two eastern Tennessee watersheds.²² The occurrence or degree of ranaviral disease or chytridiomycosis in infected individuals is unknown because animals were not collected for necropsy.

Batrachochytridium dendrobatidis (Bd) infection has been detected in captive and wild hellbenders.^3,25 In both populations, Bd has been confirmed by polymerase chain reaction (PCR) assay in hellbenders that were not showing any clinical signs of illness. However, in captive hellbenders that become severely compromised, Bd may have an augmented effect and may contribute to the death of the animal. Bd is most consistently detected by scraping the foot pads, presumably because this site has keratinized epithelium, which the fungus requires for invasion. The ventral aspect of each foot is stroked five times with an appropriate swab (wooden or plastic, depending on the laboratory’s preference) and submitted to the laboratory for PCR assay. Comparative testing of swab sites on the body has confirmed that this approach produces the most consistent results.

Saprolegniasis has been reported both in wild¹¹ and captive⁶ hellbenders. This common water mold is most commonly associated with egg mortality. In larvae and adults, infections are usually cutaneous; however it is possible for the fungus to invade into deeper tissues and potentially contribute to death.

Several gastrointestinal parasites have been detected in hellbenders, including the nematodes Spironoura wardi, Zanclophorus variabilis, Falcaustra catesbeianae, Urodelnema mackini, and Kamagainema cingula,¹⁰ the trematode Telorchis cryptobranchi,²⁴ and the cestodes Crepidobothrium cryptobranchi and Ophiotaenia cryptobranchi,²⁴ but none appear to be clinically significant. The leech (Placobdella cryptobranchii, previously Batracobdella cryptobranchii) is often present on Ozark hellbenders¹⁵ and may be the vector of Trypanosoma cryptobranchi.¹⁴ Leeches may be present in large numbers and attachment points may produce small cutaneous wounds. Trypanosoma cryptobranchi¹⁹ hemoparasites have been detected in hellbenders; however, the clinical significance is unknown (Fig. 34-1).

Figure 34-1 Trypanosoma cryptobranchii in a blood smear from an Ozark hellbender (hematoxylin and eosin stain, 40× objective).

(Courtesy J. Merkel.)

Noninfectious Conditions

Traumatic injuries to digits and appendages appears to be relatively common, presumably from intraspecific aggression and predator injuries. Wild hellbenders are frequently found missing digits or limbs.^11,13,27 In most cases, the animals do not appear to be compromised from these injuries and healing is complete. In captivity, such wounds may occur from intraspecific aggression, trauma, or exhibit materials (rock substrate). On some occasions, distal appendage wounds are difficult to heal, remain open and ulcerated, and local infection of tissues may progress to expose bone. This may be related to the captive environment if bacterial contamination is high, water quality is not correct, or temperature is inappropriate; however, similarly appearing wounds have been reported in wild hellbenders. These lesions are similar to the ulcerative syndrome caused by ranavirus, which results in necrosis of distal digits. They are also similar to a distal limb necrosis resulting in exposed bone; this has been reported in newts associated with Batrachochytrium infection.¹ Tissue samples collected from numerous affected hellbenders have been negative for ranavirus. Samples are inconsistently positive for Bd; however, most Bd-positive hellbenders do not have ulcers. The cause and pathogenesis of this condition is not clear. In most cases, antibiotic therapy is required to achieve healing. Antibiotic soaks do not seem to be as therapeutic as injectable treatment regimens. In wounds with protruding bone, surgery is required to obtain healing. Use of recombinant human platelet-derived growth factor becaplermin (Regranex Gel, OMJ Pharmaceuticals, Raritan, NJ) appears to enhance wound healing by causing rapid granulation of wounds, followed by epithelialization.

Nutritional diseases occur commonly in amphibians in captivity because of difficulty mimicking natural diet. These often include inanition, obesity, steatitis, vitamin deficiencies (B and D), and mineral imbalances, including metabolic bone disease.⁴ However, none of these diet-related diseases have been documented in hellbenders.

Congenital abnormalities may occur in amphibians because of environmental disturbances during embryonic development. In hellbenders, missing, fused, or supernumerary digits and a bifurcated limb have been documented.²⁶ In other species of amphibians, this type of defect is attributed to infection with metacercariae⁶; however, the cause in hellbenders has not been defined. It is presumed that more animals with severe abnormalities do not survive.

Neoplastic diseases are common in amphibians.⁸ In hellbenders, epidermal papilloma, squamous cell carcinoma, Sertoli cell tumor, and a poorly differentiated sarcoma have been documented.^9,11,23