Written by Dr. Stephen J. Hernandez-Divers
The Thai water dragon, Physignathus cocincinus, originates from the lowlands and highland forests of India and eastern Asia and seldom strays far from fresh water (Barnard, 1996, Rogner, 1997). It is a powerful lizard belonging to the family Agamidae. This species may reach 90 cm in total length of which more than half is tail. The dorsal surfaces are green, darkening on the joints of the limbs and the head. Along each side of the body are three to five narrow light bluish green stripes running from the dorsal to the lateral margins of the coelom. These stripes become less distinct as the lizard matures and may be lost in some adults. The ventral underside is white to pale green. The tail has alternating vertical stripes of dark and light bands and becomes progressively darker towards the extremity. A second species, the eastern water dragon, Physignathus lesuerurii, from Southern New Guinea and Australia, is slightly larger (up to 100 cm), less colorful and less common in captivity.
The Thai water dragon has remained a popular pet lizard for many years. A small size and generally quiet disposition are attractive features of this species that offer distinct advantages over its larger, more pugnacious South American cousin, the green iguana, Iguana iguana. Thai water dragons are increasingly bred in captivity and owners should be encouraged to utilize this source in preference to imported wild stock. Captive bred animals are usually healthier and more adaptable to the captive environment.
This largely arboreal lizard prefers forested areas in close proximity to freshwater lakes and streams. In captivity, large spacious tropical enclosures are required (Corborn, 1996, Vosjoli, 1997). Exhibits should be of sufficient height to allow the inclusion of several strong branches and of sufficient floor area to permit the installation of a large bathing area. In general, one to three animals require an enclosure of 2 m high x 1.8 m long and 1 m deep (Divers, 1999). The vivarium can be constructed from fiberglass, plastic or melamine-coated wood. Wooden vivaria must be treated or coated to prevent moisture damage and all internal edges sealed using non-toxic silicone sealants. The arboreal activity of water dragon dictates that feeding should occur above floor level. The inclusion of shelves at various levels and connected by secured branches provides greater useable space in a defined volume and cam be used to provide basking areas and feeding platforms. There is often a tendency to reduce ventilation in an attempt to maintain vivarium temperature and humidity. This is a mistake and sufficient ventilation, typically 0.125 m 2 ventilation are per cubic meter of enclosure is advised (Divers, 1996). Glass is invariable used in exhibit design to allow observation of the animals. Unfortunately, water dragons have a reputation for failing to respect glass barriers and rostral abrasions are frequently reported. Such problems can be largely prevented by the use of one-way glass. A less expensive option requires the placement of dark tape on glass window to improve their visibility. The requirement for high humidity and constant access to water dictated the need for a large water container at the very least. Plumbing a sink or pool into the floor of the terrarium provides efficient drainage and greatly assists with cleaning the exhibit. More advanced systems often include a water supply and water circulation system. Various sprinkler and water drip devices, waterfalls and other water circulating strategies can be used to greatly increase humidity levels. The floor should be covered with paper or outdoor carpeting that can be changed or cleaned as required. Hideouts or retreats must also be provided in sufficient numbers and in various locations so that all animals have ample opportunities to display normal behaviors, including avoidance of conspecifics and humans.
Water dragons require a diurnal temperature regime. Air temperatures should vary from 77 degrees F at night to 86 degrees F during the day. Day time basking areas should be provided by both basking and background sources. Infrared heat lamps and incandescent spotlights can provide basking areas, but they must be screened from the lizards to prevent burns. On apparently successful lamp is the mercury halide Active UV heat lamp (Westron Corporation, 3590-C Oceanside Road, Oceanside, NY) that produces a high intensity broad-spectrum light that also provides ultraviolet light (290-320 nm) for vitamin D 3 synthesis. If not used, alternative sources of ultraviolet light are essential. Regular access to unfiltered sunlight is undoubtedly best, but when not possible the inclusion of several broad spectrum fluorescent tubes (e.g. Reptisun 5.0, ZooMed Laboratories Inc., 3100 McMillan Road, San Luis Obispo, CA) is recommended. Fluorescent tubes must be positioned within 30 cm of the basking areas and replaced every 6-12 months. Mercury halide lamps can be positioned up to 1 m away and need replacement every two years. Humidity is governed by temperature, water surface area and ventilation and levels of 60-90% are preferred. Environmental parameters should be closely monitored using accurate thermometers variety of microhabitats with varying gradients of temperature, light and humidity so that the animal(s) can choose their preferred environment.
Water dragons are largely insectivorous and have been reported to eat a wide variety of items including crickets, locust, earthworms, snails, beetles, beetle larvae, small fish and some plant material (Barnard, 1996, Coborn, 1996, Rogner 1997, Vosjoli, 1997). Appropriate captive diets include a variety of gut-loaded insects, particularly small locusts, crickets, wax worm larvae and mealworm larvae. Captive farmed insects have reversed calcium: phosphorus (e.g. Ca:P ratio greater than 8:1). A high calcium (and preferably zero phosphorus) supplement should be added to the food supply of the insects to ensure their adequate calcium content. In addition, insects may be coated with a high calcium supplement with a nutritional hyperparathyroidism.
Adult water dragons should also be offered fruits and vegetables, again, balanced with a reptile nutritional supplement. Juveniles should be fed daily and adults every three to five days, depending upon activity and reproductive state. Care is required to avoid overfeeding and obesity in adult lizards. Fresh water must be available at all times.
Water dragons are not social reptiles by nature and should therefore be kept singly, or in male-female pairs, or male-female-female herms. In the wild, breeding occurs from October to December but may be observed throughout the winter and early spring in captivity (Rogner, 1997, Mattison, 1991). In captivity sexual maturity occurs between three and five years of age (Rogner, 1997). However, size is probably a greater factor than age alone, and many individuals become reproductively active in their second year when they exceed 40 cm in total length (Mattison, 1991). Males in breeding condition typically develop more brightly colored chins, chest and jowls, ranging from golden yellow to deep orange. Mature males will also exhibit hemipenal bulges at the base of the tail. The hemipenal lumen can be demonstrated with a blunt lubricated sexing probe but this is seldom necessary. Courtship displays by the male typically include prominent positioning within the vivarium and head bobbing. Males will pursue females and bite along the head and dorsum to hold the female in an attempt to align cloacae and copulate. Intromission is often unobserved by owners or keepers, with first indication of gravidity being a captive female’s coelom swollen with eggs. In the wild, mature females typically excavate a deep nest site wand lay once clutch of 8-20 (typically 8-12) eggs, with newly hatched young visible from January to April. In captivity, mature females, which may hatch up to five clutches a year, require a large nesting chamber containing sandy soil. Given breeding may occur from October through to April, it is important to position a nest chamber within the vivarium during that time, or indeed at any time courtship behavior is noted. A sudden reduction in the Coelomic size of a gravid female is a clear indication to search the nesting site for eggs. Eggs are best removed and incubated in damp sandy soil (82-86 degrees F). Incubation periods vary from 60-101 days depending on the temperature (Jaunch, 1979, Mattison, 1991). Gender determination appears to be chromosomal and not temperature dependent.
Newly hatched juveniles, measuring 15 cm in total length can be reared in small groups under similar conditions to adults. Juveniles grow quickly and can reach 40-60 cm within two to three years (Mattison, 1991, Rogner, 1991).
COMMON MEDICAL PROBLEMS
The greatest ailment afflicting growing water dragons is secondary nutritional hyperparathyroidism or nutritional metabolic bone disease. Affected animals are usually immobile or pull themselves along without lifting their bodies clear of the ground. Pathological fractures and hypocalcemic tetany are not uncommon. Many cases respond favorably to improvements in husbandry and nutrition. Female water dragons appear prone to egg retention and dystocia, often in combination with a relative hypocalcemia and secondary hyperparathyroidism that may be secondary to poor nutrition or the reproductive drive to produce eggs. Dependent upon severity of signs and medical status of the female, treatment may include nutritional and husbandry improvements, medical therapy (including oxytocin or vasotocin) and surgery (salpingotomy or ovariosalpingectomy). Reproductive problems can often be prevented by appropriate husbandry and nutrition or by ovariectomy in female pet lizards. Stomatitis and gingivitis may occur due to repeated rostral trauma or poor nutrition. Improving the perception of glass barriers and the judicious use of multivitamin supplements are often effective. Secondary bacterial infection is not uncommon and osteomyelitis of the maxilla and mandible worsens the prognosis. Digits and tails may be lost due to conspecific trauma or poor handling techniques. Topical cleansing of the wound may be all that is required but secondary infection and abscessation are frequent. Lizards kept in overcrowded and unhygienic conditions are predisposed to abscesses particularly of the limbs and head. Surgical removal of the entire abscess is typically curative, but improvements in husbandry and hygiene are required to prevent recurrence. Lizards that are overfed, kept in small exhibits and poorly exercised regularly become obese. Enlarged fat bodies and sever hepatic lipidosis are common findings. Careful nutritional control over many months is effective. Prevention involves balancing feeding with nutritional requirements and typically results in adults being fed only once or twice per week.