Environment and Husbandry for Amphibians
Captive amphibians require proper environmental conditions to remain healthy. Natural stressors, including temperature change, food availability, and habitat loss, combined with anthropogenic stressors, such as exposure to pesticides, fertilizers, heavy metals, nitrogenous wastes, and acidification, likely increase amphibian susceptibility to disease, contributing to the large population losses documented in recent years. As ectotherms, amphibians thermoregulate by shuttling back and forth between different temperatures in their environment. The range of temperatures necessary for proper metabolism, called the preferred optimal temperature zone (POTZ), varies among species. Metabolism, including the regulation of immune function and digestion, can be adversely affected if animals are kept at temperatures outside of their POTZ. Infectious diseases and malnutrition are common problems in tropical amphibians kept at suboptimal temperatures.
Amphibians require moisture to prevent desiccation. Aquatic amphibians may be accommodated in aquariums with appropriate areas for swimming. Terrestrial amphibians need a shallow container of water in the enclosure. Moisture may also be provided by incorporating small streams, waterfalls, or ultrasonic humidifiers into enclosures, or by misting frequently with a spray bottle. Because amphibians have a semipermeable skin that readily absorbs potentially harmful substances, the water must be clean and free of toxins such as chlorine, ammonia, nitrite, pesticides, and heavy metals. Chlorine can be removed from tap water by placing the water in a barrel and circulating it through a carbon filter for ≥ 24 hr before use. Some municipal water supplies may include chloramines. The chloramine bond must be split with specific dechlorinizing agents, after which water can be filtered to remove the chlorine. External canister filters or under-gravel filters help maintain water quality in tank waterfalls, streams, and ponds.
Substrates that can be used include gravel, soil, sphagnum moss, and mulch. Gravel should be either too large to be swallowed or small enough to be easily passed in the feces. Soils with chemical additives such as fungicides must not be used. Substrates such as sphagnum moss, untreated hardwood mulches, and leaf litter can be used, but cedar and pine mulches have toxic oils and should be avoided. Some amphibians cannot tolerate low pH and may develop skin irritation if they come into contact with peat moss and sphagnum moss. Heating soils to 200°F for 30 min is recommended to kill arthropods, such as trombiculid mites, and helminth parasites. Freezing substrates at <32°F also effectively removes many infectious organisms.
Adequate ventilation (1–2 fresh air changes/hr) is needed to prevent disease in amphibians. Live plants are recommended furnishings for terrestrial amphibians as they purify the air, remove organic wastes in the soil, filter light, generate humidity, and provide hiding and perching places. Aquatic plants oxygenate the water, remove nitrogenous waste, provide hiding places, and are often a source of nutrition for larval amphibians. Full-spectrum lighting using bulbs that emit biologically active ultraviolet-B (280–320 nm) is recommended to prevent metabolic bone disease. Bulbs must be changed every 6–8 mo or according to the manufacturer’s specification.
Longterm maintenance of most captive amphibians requires live food. Although most adult terrestrial and aquatic amphibians feed on invertebrates, including earthworms, bloodworms, black worms, white worms, tubifex worms, springtails, fruit flies, fly larvae, mealworms, and crickets, some amphibians feed on vertebrates and require live minnows, guppies, goldfish, or neonatal mice or rats. Vitamin and mineral supplements are necessary to prevent nutritional disease. These are commonly administered by “gut loading” insects, using commercially available diets high in calcium or by coating insects with powdered multiple-vitamin preparations that include vitamin D3 and calcium (also known as “dusting”).
Bleach (30 mL/L of water) can be used to disinfect tools and housing materials. A minimum of 30 min of contact time is recommended, after which the tools should be thoroughly rinsed with fresh water and preferably dried before use. Several sets of tools should be kept on hand when working with more than one colony of animals. Humidifiers and spray bottles must be disinfected weekly to remove potentially pathogenic bacteria, including Pseudomonas spp and Aeromonas spp.