Amphibians make up a vast group of species with over 4000 species of frogs, toads, newts, salamanders, and sirens. New species are continuously found, creating new and exciting discoveries for science and medicine research. These species are divided into the orders of Anura, the frogs and toads, Caudata or Urodela, the salamanders, newts, and sirens, and Gymnophiona or Apoda, the caecilians. This handout will focus primarily on the captive husbandry of the family of Hylidae, or true “tree frogs”. These frogs inhabit the temperate to tropical regions of the Americas, Australia, and parts of Asia and Europe. Some commonly kept pet species are the White’s tree frog (Litoria caerula) from Australia, Red-eyed tree frog (Agalychnis callidryas) from Central and South America, and the Cuban tree frog (Osteopilus septentrionalis) from North America. Most tree frogs are small in size, with adult sizes ranging from less an an inch in length up to 5 inches, most averaging 2-3 inches. Lifespans range from short for some at less than 3 years and up to 15 years for some Australian species. Tree frogs are nocturnal species that are primarily active at night, where they will hunt and feed and spend day time hours hiding in foliage or basking to thermoregulate body temperature as needed. A frog’s skin very sensitive and is specially adapted to absorb water, therefore they will not drink through their mouths. Oxygen from the air or water dissolves in the film of mucus secreted by the skin into the blood capillaries and into the blood stream, this in addition to the lungs, allow a frog to breathe.
Tree frogs inhabit various environments and have adapted to living alongside humans. In captivity, they are hardy and thrive when given proper conditions making them relatively easily kept. Size of enclosure is important to provide opportunity for the frog to climb and move around during active hours. A 20 gallon aquarium with a screen top provides adequate space a single frog or a pair. Terrariums such as a ZooMed terrarium, provide multiple size options for larger group situations and more favorably, taller options versus standard horizontal tanks. Housing multiple tree frogs can be accomplished but requires more diligence from the owner to ensure that each animal is receiving adequate nutrition and is not intimidated by cage mates. Males should not be kept together due to aggression, however a male-female pair or male with a few females as a small group are usually kept without issue. Frogs only of similar size can be kept, as smaller frogs may be eaten if small enough or injured and should be housed in large set ups to decrease stress and any aggression. Enclosure set ups can be made simple and functional to quite elaborate and more naturalistic. A simple enclosure can be made utilizing artificial plants, climbing branches, vines, and a water source with paper towels or reptile carpet substrates. From a practical stand point, this is the easiest setup for owners to maintain and is ideal for quarantine or “hospital” tanks when housing new or debilitated animals, as substrates can be replaced or cleaned daily if needed.
More complex set ups can be created with safe live plants, multiple layers of separated substrates (raised plastic grating covered by smooth gravel, topped with sphagnum moss, rehydrated sheet moss, or hardwood mulch/moss mixture) to allow drainage of excess moisture. Soils are not recommended as they are irritating, drying, and can cause issues if ingested. Soils that contain surfactants, manure, fertilizers, aerating agents, or other chemicals are potentially dangerous. Complications of impaction (GI blockage) of substrate can occur if substrate is ingested. The naturalistic set ups, if established correctly, can have beneficial microorganisms and help breakdown waste but care is needed to ensure the vivarium is not overcrowded and the biological load is not too great. If a balance is not met, the environment can quickly become toxic for the frogs to live in. Substrates in these set ups should be partially replaced at least every few months and spot cleaned regularly. Soaps and detergents should not be used to clean enclosures as residue can be absorbed through the skin. A dilute bleach solution can be used to disinfect enclosures but must be thoroughly rinsed.
Most tree frogs thrive in temperatures ranging between 75—85°F (24-30°C), that may fluctuate dependent on species. A temperature gradient is needed to allow a frog to seek different temperatures throughout the day. They will move from place to place to thermoregulate body temperature. This is done by providing a basking area on one side of the top of the cage with a low wattage ceramic heating lamp or incandescent bulb. An under tank heat pad can be added if additional warmth is required. Adequate humidity is needed for tree frogs and is easily maintained through daily misting of the enclosure with dechlorinated water. Mosses also allow for sustained humidity but care should be taken to not allow the enclosure to become continuously overly damp as this can create skin problems. Relative humidity above 70% is best for most tree frogs. Fogger systems can be helpful in maintaining humidity but must be routinely cleaned to prevent build up of bacteria or mold within the mechanisms.
Another aspect to cage design that is of vital importance is special ultraviolet-B (UVB) lighting. This can be supplied in a compact florescent bulb, florescent linear (strip) bulb, or mercury vapor bulb (which emits heat and should be monitored for excessive temperatures). Most vertebrates synthesize vitamin D3 via exposure of UVB radiation from sunlight which plays a crucial role in regulating calcium metabolism and many other biological functions. In captivity, this addition is critical in preventing vitamin D3 deficiency, where the animal is prone to illness from a weakened immune system, and calcium deficiency (which leads to Metabolic Bone Disease), where fractures occur from a very fragile skeletal system. Tree frogs should receive 10 to 12 hours of UVB light and should be at least 12-18 inches from the animal to ensure they receive exposure. Like the basking site, this lamps should be located where they can receive a gradient, therefore, placing it near the basking light allows for replication of natural sunlight and warmth from a specific site, with the ability of the frog to move away when desired. These UVB bulbs should be replaced every 6-12 months, preferably every 6 months, to allow the most benefit from the light. Even if the bulb is still functioning and emitting visible light, the amount of UVB declines rapidly.
Wild tree frogs consume a variety of food items and this creates varied vitamin, mineral, amino acid, and fatty acid intake that is hard to replicate in captivity. The most easily fed prey are domestic crickets and roaches. Wild insects or other food items should never be fed. Young frogs should be fed 3-4 times weekly and adults 2-3 times weekly. Small thawed frozen pinkie mice can be offered occasionally, but less often due to obesity concerns. Food items with hard exoskeletons, such as mealworms, should be limited due to risk of injury to GI tract. Frogs swallow food essentially whole, therefore appropriately sized food items should be offered.
In order to fortify the captive diet, supplements are added to ensure proper nutrition. Calcium powders are important to ensure the proper ratio of calcium to phosphorus is consumed. Generally, a ratio of 1:1 or 1:2 (Ca:P) is recommended to prevent nutritional diseases. A diet that is too low in calcium or too high in phosphorus can result in Metabolic Bone Disease. We recommend ZooMed Repti-Calcium with D3 added. This supplement should be offered by dusting food items 2-3 times weekly.
A multivitamin as also needed to ensure adequate levels of vitamin A are consumed. It is an important vitamin, essential to good eye and skin health. Not all multivitamins contain the pre-formed vitamin A (retinol) which is from animal sources. Commonly, pre-vitamin A nutrients (carotenoids, mainly beta carotene), from plant sources are used and further research needs to be conducted to understand if reptiles and amphibians can utilize this vitamin A source. It is known however, that the retinol-sourced form is converted. We recommend the multivitamin powder, ZooMed Reptivite. This supplement should be dusted on food items once every week for juveniles and once every other week for adults.
Fresh, clean dechlorinated water should be available at all times. Water should be free of chlorine, chloramine, ammonia, and heavy metals. Tap water should be aged by letting it sit in an open container for 24 hours before use. Water conditioners are not recommended for use for preparing water for amphibians.
Metabolic Bone disease — As mentioned above, this condition is a complex disease involving an imbalance of vitamin D3, calcium, and phosphorus as well as lack of UVB exposure, that cause issues during bone development. This results in deformities of the skeletal system, often permanent even when resolved. Fractures, scoliosis (curving of the spine), and jaw deformities (soft, pliable jaws) are common. UVB is especially important in helping vitamin D3 activate in the skin, which helps the body take calcium and utilize it towards bone formation and maintenance.
Chytridiomycosis (Chytrid) — A highly contagious fungal disease of amphibians that affects the skin, specifically keratin, the protein that helps make the skin tough and resistant to injury. The skin thickens (hyperkeratosis) which alters the normal ability of the frog to absorb necessary water and electrolytes to sustain life. Lesions and sloughing of the skin surface are common. Signs also include abnormal posture, lethargy, and neurologic issues. This disease is often deadly and is able to survive in the environment, therefore good sanitation practices are especially important to prevent spreading the disease. Wild food items can spread this disease if fed. There currently is no treatment for this infection.
Ranaviral Disease — Viral infections of the genus Iridovirdae, cause systemic infection that cause lethargy, emaciation, skin ulcers, hemorrhaging of the internal organs, and often death. Frogs can be carriers of the disease and show no clinical signs. The virus is transmitted through contact between carrier frogs to other frogs as well as through a contaminated environment. Sanitation practices are important in preventing infection from spreading. Wild food items can spread this disease if fed. There currently is no treatment for this infection.
Salmonellosis — Frogs carry Salmonella bacteria that can cause serious illness in people after handling or contact with amphibian environments. Proper hygiene is important to prevent contracting this disease. Washing hands and surfaces where any frog has contacted with soap and water or disinfectant will help prevent infection. Young children and immunocompromised individuals are especially at risk.