Nutritional secondary hyperparathyroidism (NSHP) is one of the most common nutritional diseases affecting captive amphibians. Ramsey Canyon leopard froglets (Rana subaquavocalis) head-started at the Phoenix Zoo, developed signs of NSHP that was associated with low calcium hardness (calcium carbonate) in the enclosure water of the tadpoles. Reversal of the clinical signs was achieved by adding vitamin D3 and calcium gluconate to the enclosure water of the froglets.
The Phoenix Zoo has been involved in head-starting programs for native ranid frogs for several years. In 2000, an egg mass of the endangered Ramsey Canyon leopard frog (Rana subaquavocalis) was brought in for the head-start program. In previous years, water quality parameters were not monitored. In 2000, significant changes were made to the husbandry practices that included a different filtration system and monitoring of the temperature, pH, ammonia, nitrite, nitrate, total hardness, and calcium hardness on a regular basis. As in previous years, the majority of the husbandry was performed by the Tadpole Task Force, a group composed entirely of volunteers. (See www.tadpoletaskforce.homestead.com for more information on this process) (VIN editor: link could not be accessed on 2/25/21).
Due to the number of tadpoles involved, it is difficult to monitor the individual progress of any individual specimen. Lacking water quality data from previous years, attempts were made to maintain the water quality parameters at “neutral” levels. For calcium hardness, levels were maintained below 200 ppm most of the time. At the time of metamorphosis, several froglets developed hydrocoelom, gastrointestinal bloating, or tetany following exercise. Some froglets died without signs. These signs are consistent with hypocalcemia, so a sample of affected froglets were evaluated radiographically. Portions of the urostyles and lateral processes of the vertebrae were radiolucent and overall bone density was lower than normal. The vertebral bodies, endolymphatic sacs that accumulate calcium, were radiolucent. The presumptive diagnosis was nutritional secondary hyperparathyroidism (NSHP). Nutritional secondary hyperparathyroidism is the most common nutritional disease of amphibians reported in one pathology survey.1 A thorough review of previous years’ husbandry practices revealed that calcium carbonate and mineral blocks had been added to the tank water. Although the calcium hardness of the water had not been measured in prior years, the tadpoles were frequently seen resting on the calcium blocks. This had not occurred in 2000.
Due to the number of froglets involved, it was not practical to individually administer oral calcium and vitamin D3. Calcium and mineral blocks formulated for tropical fish were added to the tank water. In addition, since these are highly aquatic frogs, the treatment plan consisted of a baths of approximately 2.3% calcium gluconate solution and 2–3 IU/ml of vitamin D3 (High-D 2X Dispersible Vitamin D3 Liquid Concentrate, 4,000,000 IU/oz, Russell Company, Laboratories, Longmont, CO, USA). The undiluted vitamin D3 product may cause hypervitaminosis D in humans through skin contact, and anyone handling the product wore disposable latex or vinyl gloves. The gloves were thrown away after use. Once the product has been diluted in water, it is safe to touch the medicated water with bare hands. Initial treatments were performed in a separate bucket when the froglets were removed from their enclosures for cleaning, approximately every 3 days. They were maintained up to 4 h in the calcium and vitamin D3 solution. This regimen was changed to a continuous bath after no change was detected radiographically at 6 wk, although signs of hypocalcemia had abated. This solution was freshened whenever their tanks were cleaned, a minimum of three times per wk. Over the following 16 wk, the frogs showed gradual increase in bone density and were radiographically normal at the end of the season.
Unfortunately, NSHP continues to be a common problem in captive amphibians. Although this is traditionally associated with problems of prey nutrient composition (i.e., inverse calcium:phosphorus ratios, low total calcium, lack of vitamin D3), this experience suggests that Ramsey Canyon leopard frogs obtain some of their calcium requirements from their aqueous environment. Data obtained from natural ponds in 2001 revealed a calcium hardness of 250–300 ppm (27 March 2001, Bernstein Pond), approximately 50–100 ppm higher than the average calcium hardness maintained throughout 2000, prior to the presumptive diagnosis of NSHP. Although amphibian skin is permeable to calcium and fat-soluble vitamins, there is no way to know if the treatment administered was absorbed topically, ingested or a combination of both.
This case report illustrates the importance of obtaining water quality data on natural breeding sites of amphibians in order to provide optimum conditions for captive propagation and husbandry of offspring.
I would like to thank Keri Means, TTF coordinator, the entire team of the TTF, Tara Sprankle, Roger Cogan, Dan Adikes, and Kay Fielding for their involvement in the Ramsey Canyon leopard frog recovery project. The Ramsey Canyon Leopard Frog Conservation Team includes the U.S. Fish and Wildlife Service, Arizona Game and Fish Department, U.S. Forest Service, U.S. Army, and the Nature Conservancy.
1. McWilliams, D.A. 2000. Analysis Overview: Nutritional Pathology Survey. Department of Population Medicine, Ontario Veterinary College, Guelph, ON, Canada.