General Recommendations for Installation and Maintenance of the Amphibious Enclosure

Glues and Sealants. Only glues approved for aquarium applications should be used in amphibian enclosures. New constructions should be thoroughly cured, and then soaked for several days in repeated baths of clean water to reduce harmful levels of contaminants. Whitaker (1993) describes hyperactivity in a large number of poison frogs (family Dendrobati- dae) exposed to PVC pipes that had been freshly glued with PVC cement.

At NAIB, the two-part epoxy paste “PC-7” (Protective Coating Co., Allentown, PA) is used to repair crack lines in plastic aquariums, to attach bulkheads to glass and plastic tanks, and to glue various porous and nonporous amphibian cage furnishings together. This epoxy is easy to work with, has a long setup period, and bonds well even when rather imprecisely measured and mixed. A similar product by the same company, “PC-11,” can be used on wet surfaces. Aquastick™ (Two Little Fishies, Inc., Coconut Grove, FL) is another safe epoxy paste that comes premeasured for use. It has the advantage of attaching to damp surfaces and curing underwater. Any time an epoxy is used it should be allowed to completely cure for at least 24 hours, and the cured epoxy should be flushed with clean water several times before placing the item in contact with a living amphibian.

Water Quality. The water used in an amphibian enclosure should be free of harmful substances such as chlorine, chloramine, ammonia, and heavy metals. Although most adult amphibians are tolerant of fairly high levels of chlorine, eggs and larvae may be extremely sensitive. It is recommended that tap water intended for use with amphibians be run through an activated charcoal filter or aged for at least 24 hours in an open container to outgas the chlorine. The addition of an air stone will greatly speed up the aging process. Caution should be used following the addition of a water filtration system, as the mineral content of the water may be altered in addition to removing chlorine. As an example, tadpoles of the dyeing poison frog, Dendrobates tinctorius, were raised successfully in aged tapwater at the Philadelphia Zoo, but tadpoles from the same parents who were offered the same food developed spindly leg when raised in carbon-filtered water. Switching back to aged tapwater eliminated the spindly leg problem in subsequent batches of tadpoles. Although spindly leg has been noted in various dendrobatids at the National Aquarium in Baltimore, a clear link to the use of carbon-filtered water has not been demonstrated.

It is recommended that water conditioners sold for use with tropical fish not be used for preparing water for amphibians. O’Reilly et al. (1995) report that tap water treated with conventional chemicals used for tropical fish is often fatal to the Rio Cauca caecilian, Typhlonectes natans, the most commonly sold caecilian in the United States. Also, some water conditioners reduce or remove medication dyes such as malachite green, methylene blue, and potassium permanganate, and thus could interfere with a medical treatment.

Completely deionized water is harmful to aquatic amphibians, as the effort needed to maintain the osmotic balance of their body tissues cannot be sustained long against such a gradient. Artificial pond water consisting of distilled or reverse osmosis water and mineral additives has been used with much success with aquatic amphibians (see Table 24.1.). Bottled spring water is also commonly used with amphibians. Any new water added to an amphibian enclosure should be the same temperature as that in the home tank to avoid thermal shock to the animals. (See Chapter 12, Water Quality.)

If water is offered in a bowl to amphibians, it is imperative that the water be clean. Bacteria can colonize water bowls quickly, and at an even faster rate when the water is contaminated with feces, food, or shed skin. This mandates that the bowl be cleaned daily and disinfected several times weekly to reduce the chance that the bowl will be a source of pathogenic organisms (see Wright, 1993, for information on disinfectants). Keeping an emergent rock in the water bowl will allow any food insects that fall in to escape. Drowned insects quickly pollute the water.

Substrate. A medium-grade gravel substrate can serve as an excellent biological filter in an amphibian enclosure. The gravel should either be too large for the amphibian to ingest or so small and smooth that it can be passed through the digestive tract. Otherwise, the amphibian may suffer complications arising from a gastrointestinal foreign body impaction. It is wise to use smooth gravel to minimize the possibility of damage to the amphibian’s delicate skin, especially if the animal tends to dig. Smooth gravel will also minimize internal damage and facilitate passage, should the amphibian ingest some of it. The gravel should be of a color typical of the animal’s natural habitat. For many ground- and rock-dwelling amphibians, this means that the animal will blend in with the substrate. This camouflage is not only interesting to observe, but presumably helps to make the amphibian feel less vulnerable and less stressed.

If sand is to be used to overlay the gravel, it is better to use horticultural silver sand rather than builder’s sand. The latter tends to form a crust after it has been dampened and dries. It is recommended that soil or potting mixes be used sparingly, unless essential to the lifestyle of the amphibians being kept (e.g., fossorial or woodland species). A soil substrate is more work to service and drains less well than a simple gravel substrate covered with moss or leaf litter. With proper planning, it is possible to create a lush planted enclosure using soil just around plant roots, or using epiphytic plants (which require no soil) and rehydrated dried mosses and leaf litter (Plate 5.1).

If soil is used over gravel, a layer of fiberglass window screening can be sandwiched in between to prevent the soil from clogging up the gravel layer. Weed guard fabric, available in hardware and garden stores, can also be used for this purpose, but tends to clog up with tiny soil particles over a period of months.

Many commercially sold topsoil and potting mixes are unsuitable for amphibian enclosures because they contain potentially dangerous chemical additives. These include surfactants for moistening the soil, antifungal agents, fertilizers, and aerating agents that are potentially dangerous if ingested (e.g., perlite, styrofoam). Manure-containing compost should be avoided altogether, because it is too acidic and there are often undesirable chemicals present. Peat moss and potting mixes containing peat moss should be avoided. They are too acidic for many amphibians and will irritate their skin. Caecilians, in particular, are very sensitive to contact with peat (O’Reilly et al., 1995).

When soil is used, the composition should match that of the amphibian’s natural habitat. For example, the spadefoot toads, Scapbiopus spp. and Spea spp., do best in sandy, loamy soil, whereas lungless salamanders (family Plethodontidae) prefer rich, organic soil that is pH neutral.

Soil of appropriate composition can be collected in the field, so long as it is free of contaminants (e.g., motor oil, gasoline, pavement salt, paint). Generally, there are few negative health implications of using clean but not sterile soil. Some of the organisms present in the soil, in fact, may help to keep the vivarium healthy, breaking down waste products from the amphibians and dead plant material. However, if one wants to be absolutely safe against possibly exposing a captive amphibian to undesirable organisms, such as trombiculid mites, the soil should be heat- or cold- treated. Heat treatment is often effective in killing arthropod parasites, and may also destroy the ova of helminth parasites. The soil being treated should be arranged in a layer no more than 2.5 cm (1 in) deep, and baked at a temperature of at least 95°C (200°F) for 30 minutes or more. Alternatively, exposing the soil to temperatures well below the freezing point of water (0°C, 32°F) for several weeks may kill soil arthropods. Another option is to place the soil in a dark plastic bag and place it in strong direct sunlight for several hours.

Wood rot (crumbled wood from decaying logs) is an excellent substrate for many woodland amphibians. Fresh material may even contain invertebrate species that are nutritious food for the captive amphibian. Again, however, one must weigh the benefits of using a living substrate against the possibility of introducing undesirable invertebrates and disease into the captive environment. If wood rot is desired to be pest free it can be treated by freezing or by placing it in a dark plastic bag in direct sunlight. Oven treating may cause the wood to char or otherwise alter its composition.

The soil in a vivarium should drain readily, so that pools of water do not form in it. Also, the soil should have a moisture gradient, so that the amphibian can carry out normal osmoregulatory functions (see Section 5.6.2, Humidity). The range of the moisture gradient that should be provided will depend on the particular requirements of the species being housed.

If an amphibian appears to avoid the soil in its enclosure (e.g., if a fossorial species stays on the surface), or shows signs of contact irritation (i.e., erythema of the ventral surface, inappetence), the moisture content or soil composition may be inappropriate and the soil should be replaced.

Ground Cover. Common ground covers include live moss, rehydrated sheet and sphagnum moss, hardwood mulch and nuggets, and leaf litter. All of these materials, except for the leaf litter, can be purchased at garden centers.

Properly maintained, these substrates will develop a complex community of beneficial microorganisms that will help to keep the substrate “healthy,” breaking down waste products from the amphibians and dead plant material. Of course, this living system will fail if the vivarium is overcrowded and the bio-load is too high. A balance must be found. Prompt removal of large droppings by hand is recommended, with spot replacement of heavily soiled or decomposed substrate at least every few months.

Living mosses often do poorly in vivariums because the light levels tend to be inadequate and moisture levels too high or too low. Some amphibians (e.g., some specimens of terrestrial caecilians) appear to be irritated by prolonged contact with sphagnum moss or sheet moss (O’Reilly et ah, 1995).

Sphagnum moss is considerably less expensive than sheet moss. Moist sphagnum is an affordable solution when a substrate is needed for temporarily housing a terrestrial or fossorial anuran or salamander, as, for example, during a medical procedure or quarantine. The major disadvantages of sphagnum are that it crumbles easily (small pieces stick to amphibians and are easily ingested with prey items), and it is easily tracked into the water. As the sphagnum decomposes and packs down (over a period of many weeks), water and wastes do not pass through it readily, and it may become a breeding ground for undesirable anaerobic bacteria. However, when kept moist and changed regularly, it can be used over a long period of time to house many species of amphibians.

Sheet moss is expensive but attractive. It can be arranged to form a smooth, carpetlike substrate which gives food insects few places to hide and facilitates their capture by surface-feeding amphibians. Moreover, the structural integrity of sheet moss reduces the chances that the amphibian will accidentally ingest moss during food capture.

A tight carpet of sheet moss is useful for stabilizing the bank along a stream or pond, and for preventing an amphibian from tracking debris into the water.

Cedar and pine mulches and nuggets should be avoided, as they contain natural compounds that are potentially toxic to amphibians. Only untreated hardwood mulches should be used. Care should be taken to remove from mulch any shards of wood that could injure the amphibian. Mulch retains moisture well and aids in humidifying the vivarium. The mulch should be replaced at least every few months.

Freezing or sunlight sterilization are the best options for treating moss, leaves, and bark to rid them of undesirable organisms.

A heterogenous substrate may be needed to accomodate different aspects of an amphibian’s behavior from tunneling in soil to foraging underneath dry leaves. The natural world is rarely a homogeneous environment, and neither is the healthy vivarium.

In some instances, it may be desirable to house amphibians on a substrate of moist paper toweling (see Section 5.5.8, Terrestrial Forest Floor Enclosures). Unbleached paper toweling is a very hygienic substrate when fresh, but it degrades rapidly and organic wastes accumulate on the surface. Many amphibians are restless and seemingly stressed on a paper towel substrate, although others (e.g., many species of terrestrial salamanders) do fine on it (see Section 5.5.8). Providing hiding spots in the form of crumpled balls of paper or folds in the towel substrate may relieve the stress experienced by some individuals.

Plants. Plants, whether artificial or living, serve many functions in the vivarium. They provide cover and rest spots, elevated perches for territorial displays, sites for oviposition in some terrestrial and arboreal species, and they act to filter the overhead light, creating the more subdued lighting at ground level that most amphibians prefer. Live plants provide additional benefits over artificial plants. Some common indoor plants help purify the air and utilize organic wastes in the soil (Raloff, 1989). Live plants also increase the humidity in an enclosure. Aquatic plants help to oxygenate the water and rid it of harmful organic wastes.

Both terrestrial and aquatic plants can be rooted directly into the substrate, or they can be placed in individual pots that are buried in the substrate. Keeping plants in their pots facilitates cage cleaning and replacement of old plant material, with a minimum of disturbance to the cage inhabitants. Also, pots protect plants against amphibians that tend to dig. Plastic pots are preferable to terra cotta for the former are lightweight, nonabrasive, non-absorbent and easily cleaned.

Plants that thrive in low light levels are recommended for amphibian enclosures, where subdued lighting is most appropriate. Hardy terrestrial plants that are especially tolerant of low light include the peace lily, Spathiphyllum tasson, the emerald beauty, Aglaonema commutatus, the silver queen, Aglaonema roebelinii, golden pothos, Epipremnum aureum, and the dwarf palm, Cbamaedorea elegans. An extensive review of plant species appropriate for the vivarium is given in Mattison (1993b).

Many of the common vivarium plants contain oxalates. If consumed by prey insects, there is a potential for these oxalates to create problems in the amphibians consuming the insects. It is preferable to release only as many plant-eating feeder insects into a planted amphibian enclosure as can be eaten within a few hours. When crickets are being offered, a small dish of cricket food can be placed in the enclosure to offer the insects an alternative to eating the vivarium plants. Commercially prepared cricket food, which is fortified, will also boost the nutritional content of the feeder insects (Allen & Oftedal, 1989).

Whatever plants are used in the amphibian enclosure should be free of sharp spines and edges and stiff tips. Many bromeliads have rigid leaves with spines along the edges. Such plants could impale or cut into the delicate skin of an amphibian jumping across the enclosures or tussling with a cagemate. These plants should be avoided.

Plants that are purchased from a nursery will often be contaminated with fertilizer, pesticides, fungicides, and detergents (to enhance the shine of the plants’ leaves). The potting soil may be similarly contaminated. As a safeguard against these hazards, all plants should be removed from their original pot and as much soil as possible should be removed from the roots. The entire plant should then be thoroughly rinsed in fresh water and repotted.

Arboreal bromeliads and other epiphytes can be lightly wrapped in Osmunda fern fiber or wired to a tree fern plaque. These absorbent natural products provide an anchor for the roots, keeping them moist but not wet. Tree fern boards are derived from the stems of certain wild tropical ferns, and for this reason, one may wish to avoid using this product. Compressed peat logs are not recommended because of their high acid content.

There is a small risk that plants will be contaminated with the ova of nematodes pathogenic to amphibians. A common source of the contamination for store- bought plants is the feces of infected Cuban treefrogs, Osteopilus septentrionalis, which thrive in the greenhouses of south Florida. Unfortunately, there is no known treatment that will kill these ova without also killing the plants or contaminating the plant with chemicals deadly to amphibians. To reduce the parasite load, all soil should be removed from the plant and the plant should be rinsed well before repotting.

If aquatic plants are used, it is advisable to treat them with a molluscicide or rinse them thoroughly in fresh water to eliminate aquatic snails. Snails can serve as the intermediate host for many parasites of amphibians, and snails will eat amphibian egg masses. The plants can be soaked in a 0.25 mg/L copper sulfate solution for 48 hrs at 30°C (85°F) to eliminate any adult freshwater snails (Cardeilhac &c Whitaker, 1988). The plants should then be rinsed thoroughly in fresh water to remove all dead snails, their egg masses, and any copper residues. As an additional safeguard against copper residues, the plants should be held in copper-free water for several days before being incorporated into the amphibian aquarium. Copper-removing solutions (e.g., NovaAqua®, Novalek, Inc., Hayward, CA), are available at pet and aquarium centers.

Green algae often grows in the undisturbed pools and streams of vivariums. Green algae can be beneficial in cleansing the water, as well as in contributing to the diet of herbivorous and omnivorous larval amphibians.

Branches, Rocks, and Other Heavy Furnishings. Whenever heavy objects (e.g., rocks, branches, ceramic flower pots, large potted plants) are used in an amphibian enclosure, one must always consider the potential for injury to the cage inhabitants if there is a cave-in or the furnishings topple over.

Furnishings should be solidly built so that there is no possibility of collapse. If the amphibian tends to dig, heavy tank furnishings should rest directly on the (false) floor rather than on top of the substrate. Otherwise, the animal may undermine the furnishings and be injured or killed in a cave-in. It is also possible that glass or plastic cage walls could be damaged in such an accident.

If a rock wall or waterfall is desired, the rocks should be securely fixed together with silicon rubber or a waterproof nontoxic epoxy (e.g., Aquastick™, Two Little Fishies, Inc., Coconut Grove, FL). Attach the rocks to a frame (e.g., rigid sheet plastic), and the entire system can be removed, if needed. This can greatly facilitate cage cleaning and maintenance work on the furnishings. It also means that the configuration of the rock structure will not change from cleaning to cleaning. Familiar retreats and perches will be left intact. This constancy in cage furnishings may help to reduce the stress of cage cleaning on the amphibians.

Rocks collected in the field should be thoroughly rinsed in clean, running water before use. Branches can be sun sterilized in a sealed, clear or black plastic bag left in strong direct sunlight for a day. Alternatively, branches can be frozen to eliminate undesirable organisms. To be safe, only rocks and wood suitable for use in freshwater fish tanks should be used in aquatic enclosures. As in the case of mulches, branches should be hardwood.

Water bowls should be shallow, preferably with sloping sides. They should be tip-proof and flat- rimmed for comfortable perching. Heavy (shatterproof) unleaded glass, glazed ceramic bowls, or plastic dishes are recommended because they can be easily cleaned and disinfected. If a ceramic bowl cracks or chips, it should be discarded, because of the possibility of lead leaching out. Cracked containers also may have dangerous sharp edges, and they may harbor pathogens that are not easily removed during cleaning.

Retreats. Amphibians are secretive animals, and most spend a considerable amount of time hiding. It is essential to provide them with adequate options for such retreat or camouflage to prevent undue stress. Appropriate hiding spots should be provided at different points in the thermal and moisture gradient, so that the amphibians are not forced to choose between meeting physiological needs and security.

The type of refuge that is most appropriate depends on the species of amphibian involved. The Surinam horned frog, Ceratophrys cornuta, will camouflage itself in a layer of moss or leaf litter to avoid detection by potential predators and prey, while an arboreal red-eyed treefrog, Agalychnis callidryas, will seek refuge in lush green foliage.

Cork bark, hollow coconut shells, hardwood branches, and smooth rocks can be used to provide refuges as well as visual barriers within the enclosure. There should be a minimum of one retreat per amphibian, more if the species in question is territorial. The retreats should be scattered throughout the enclosure in areas of different temperature and humidity, so that an amphibian is able to hide in a spot with an appropriate microclimate. Cave-style retreats should not be used with species of amphibians that will not use them (e.g., the giant monkey treefrog, Phyllomedusa bicolor). For many of these amphibians, caves are havens for live prey that go uneaten.

Cork bark can serve double duty as a retreat and as a feeding platform for many species of small frogs, such as the mantellas, Mantella spp., the stubfoot toads, Atelopus spp., and the poison frogs (family Dendrobatidae). Small insects (fruit flies, hatchling crickets, springtails) can be sprinkled onto the bark, where they are easy prey for the frogs. Even if the enclosure is freshly misted, insects will not stick to the bark, because it absorbs and passes moisture quickly. Cork bark can be autoclaved for sterilization without altering its appearance.

Amphibian retreats can be fashioned from darkly colored plastic containers. Examples include plastic bowls, storage containers, plant pots, and the reinforcement cup on the bottom of many soda bottles. The chosen container is simply turned upside down, and an access hole slightly taller and wider than the amphibian is cut into the wall. The edge of the access hole and the interior surface of the retreat should be smooth, so that the amphibian cannot injure itself. The size of the retreat will depend on the number, size, and species of amphibian being housed. The retreat should be deep enough to enable the amphibian to fully hide its body inside in a relatively dark environment. Most amphibians that use hideaways prefer one with a low ceiling, so that they can wedge their body beneath it with their dorsum touching or nearly touching the ceiling. Among the possible explanations for this preference are water conservation, thermoregulation, and predator avoidance.

Similar to other amphibian habitats, aquatic enclosures should include multiple dark retreats. A subordinate amphibian should not be forced to share a retreat with a more dominant animal, and animals should not need to venture far to seek cover. Furnishings should be arranged so that when food is offered, it is relatively near a refuge, such as a submerged rock or wood cave, or section of PVC pipe.