Aquatic Pond Enclosures. Complex and Spartan Pond Enclosure

Complex Pond Enclosure. The pond enclosure is appropriate for aquatic amphibians adapted to living in relatively still or low-flow bodies of water. These amphibians include pond-dwelling larvae, neotenic pond-dwelling salamanders, aquatic newts, and aquatic frogs (Xenopus spp. and Pipa spp.). These species are often restless in an aquarium with significant water movement.

The amphibian pond enclosure requires only a slight modification of the standard fish aquarium to accommodate the need of many amphibians to breathe air.

The basic, low-maintenance pond enclosure (Figure 5.2, Plate 5.2) utilizes an undergravel filter with a gravel substrate about 5 cm thick. The filter can be operated by air lift. Alternatively, an external canister filter can be used to create a reverse flow undergravel filter. Outflow water from the canister is sent into the lift tube, to move under the false floor and up through the gravel bed. This diffuses the water current for still water inhabitants. The return water is suctioned from the water column above the gravel, on the opposite side of the tank from the tank inflow. It is important to screen the tank outflow so that the amphibians cannot be trapped by the force of its suction. A filter screen with a wide surface area is recommended to disperse the force of the uptake.

Figure 5.2. Lateral view of pond enclosure for amphibians. A. false floor assembly (see Figure 5.1 В—D). B. pea gravel layer approximately 2” (5 cm) thick. C. underwater rock cave. D. air lift tube sealed to the tank wall and false floor with silicone rubber (also serves as access port to subfloor for siphoning up debris). E. hole in the tank wall for the air line and heater cord; alternatively, a hole could be cut into the lid. F. lid (see Figure 5.1 E—H). G. aquarium heater (for additional protection, this may be sheathed in a perforated PVC pipe). FI. anchored cork bark island. E aquatic plant tall and strong enough to provide a perch close to the water surface for the tank inhabitants. J. water line. K. emergent hardwood log providing an underwater retreat and shallow water rest area. L. drain assembly (see Figure 5.1 К— M). (Sandy Barnett)

The enclosure should include shallow areas where amphibians can rest and gulp air. Many aquatic amphibians rely to some degree on pulmonary respiration and may drown if not provided with the opportunity to surface without strenuous effort. Shallow rest areas can be created by sturdy floating or emergent vegetation, smooth rocks or wood projecting at a low angle out of the water, or floating bark. For some semiaquatic species, such as the South American bullfrog, Leptodactylus pentadactylus, it is necessary to provide a large land area bordering the water to accommodate their full range of behaviors.

Similar to other amphibian habitats, aquatic enclosures should include multiple dark retreats. These refuges can be made from piled rocks, submerged wood, or sections of PVC pipe. A minimum of one retreat per amphibian is recommended, although additional retreats may be placed throughout the vivarium to allow access to a range of temperatures.

Spartan Pond Enclosure. It may be necessary to isolate an amphibian in a simple tank where the contents can be regularly replaced or disinfected. Such spartan enclosures may have no substrate, and only plastic plants and perhaps PVC piping for underwater enrichment. Floating pieces of styrofoam, plastic shelves, or plastic plants can be placed in the enclosure to create shallow water or exposed rest areas.

The dump and fill system can be used for water maintenance in the spartan tank. A siphon or water vacuum should be used to remove all uneaten food and other debris daily, and regular partial water changes are recommended to prevent buildup of ammonia and urea. The frequency of the water changes and amount of water that should be exchanged will depend on the volume of water in the enclosure and on the number, size, and species of amphibians being kept. As a starting point, a 10% water change should be made every 2 days. Change water should be aged and brought to the same temperature as the home tank water to avoid chemical and thermal shock to the amphibians.

An airstone can be added to the spartan tank to prevent scum buildup on the water’s surface and to oxygenate the water. A sponge filter can be used for biological filtration, but it should be augmented by regular partial water changes and prompt removal of gross debris, such as feces or uneaten food. Sponge filters cannot handle high levels of ammonia and are best suited to small groups of small amphibians, such as anuran and salamander larvae adapted to living in ponds. If an amphibian harbors or is suspected of harboring an infectious disease, it will be necessary to periodically discard the sponge filter, since it cannot be completely disinfected. However, sponge filters are relatively inexpensive and easily replaced. Keep in mind that the sponge filter takes time to reach peak efficiency in biological filtration, and frequent replacements will prevent this from happening. Also, the beneficial organisms in the filter may be eliminated by some medications in the water.

Another filtration option in the spartan tank is a small in- tank box filter that provides biological, mechanical, and chemical filtration, but is not strong enough to create a significant current. Such a filter can easily be disinfected, and the filtering material can be replaced at the same time. However, box filters, like sponge filters, need time to reach peak efficiency, and frequent replacement of all filter material will prevent this from happening. Also, activated charcoal eliminates certain medications from the water.

Natural porous materials are not recommended in the spartan hospital tank, as they are more difficult to clean and disinfect. If an amphibian is undergoing treatment for an infectious disease that is difficult to eliminate, the enclosure and all furnishings should be cleaned and disinfected after each treatment.

There are some exceptionally hardy species of amphibians, such as the axolotl, Ambystoma mexicanum, and the African clawed frog, Xenopus laevis, that are often successfully maintained for a long time in relatively spartan aquatic enclosures.

Spartan pond enclosures are often used for rearing pond- dwelling larval frogs to metamorphosis. Plastic plants or hardy live aquatic plants that do not require rooting in the substrate (such as Elodea canadensis) can be added to provide cover and rest areas. Living plants will also help to rid the water of harmful organic wastes. Some tadpoles will eat the vegetation, or the algae that grows on it. Cork bark, styrofoam, plastic shelves, or a sloping shore can serve as a landing for new metamorphs, as well as provide cover and a surface for algae growth.

These spartan nursery tanks require more daily maintenance than an enclosure set up with undergravel filtration, but the barren floor in the spartan enclosure can greatly facilitate the retrieval of small tadpoles. In gravel-bottom tanks, small tadpoles can be very difficult to catch, as they seek cover in between the rocks when alarmed.