Proper Lighting for the Health and Successful Reproduction of Amphibians

Precipitation. Precipitation is an essential trigger for breeding behavior in many species of amphibians (for a review, see Duellman & Trueb, 1986; Stebbins & Cohen, 1995; Zug, 1993). For tropical terrestrial amphibians, it is often the onset of the rainy season following the dry season that stimulates reproductive behavior. Flooding (associated with rain) and a drop in water temperature elicits breeding behavior in many tropical aquatic and stream-breeding terrestrial species. And among many temperate species, hibernation followed by spring rains is often the stimulus for reproduction.

Simulating these environmental cues in a captive setting is essential to successfully propagate many species of amphibians. Wright (1994) discusses various options for constructing “rain chambers” for breeding amphibians.

The basic NAIB amphibian enclosure can be modified to provide rain showers. The outflow of a canister filter is diverted into a perforated tray positioned over the cage top. The intensity of the rain shower is controlled by the number of holes in the tray, and the rate of water flow. The goal is to have a gentle rain over a portion of the tank, allowing the amphibians to avoid it if they choose to. (This pattern of rain also provides a drier area where live food insects can congregate, which minimizes insect losses due to drowning.)

If the filtration material in the canister is removed, and the unit is used strictly to move water, it can be set on a timer to automatically rain on the enclosure, as needed. A timer should not be used with a filter- loaded canister, since the system will become anaerobic if the water flow is shut down for more than a few hours, and the nitrifying bacteria will die.

Lighting. The proper illumination for health and reproductive success in captive amphibians is a subject of much debate. A conservative approach, and the one that is recommended here, is to provide lighting that mimics, as closely as possible, the spectral characteristics, intensity, and duration of light found in the amphibian’s natural habitat.

There are numerous brands of fluorescent lights on the market purporting to be “full-spectrum,” i.e., to duplicate the spectrum of natural sunlight. Of particular concern to the herpetoculturist is the emission of light in the ultraviolet-B portion of the spectrum (285-320 nm). It is well known that ultraviolet-B radiation plays a key role in the biogenesis of vitamin D₃ in the exposed skin of endothermic vertebrates (Holick, 1989). There is evidence that this is also true for at least some species of reptiles (Allen, 1989) and amphibians (St. Lezin, 1983). As a precaution against vitamin D₃ deficiency and its complications, most herpetoculturists use full-spectrum lighting (which emits ultraviolet-B radiation) over amphibians, in addition to fortifying the diet with this vitamin as part of a multivitamin, multimineral supplementation program.

Unfortunately, the amount of ultraviolet-B radiation emitted from many of the full-spectrum fluorescent lights, especially over an extended period of time, is suspect. It is recommended that whatever full-spectrum lights are chosen, they be replaced every 6-12 months. Also, the lights should be positioned no more than 46 cm (18 in) from the cage floor, since the intensity of the emissions falls off rapidly with increasing distance from the source. At NAIB, at least two 4ft (122 cm) “Instant Sun” fluorescent tubes (Verilux, Stamford, CT) are placed over all amphibian enclosures approximately 8 cm (3 in) above the screened lids. Some other bulbs have been manufactured and distributed recently that emit a higher proportion of their output as ultraviolet-B radiation (e.g., ReptiSun 310®, ZooMed, San Luis Obispo, CA; Reptile D- Light, 8% Type, Ultraviolet Resources International, Cleveland, OH) (Gehrmann, 1996), but there is no long-term track record for their use with amphibians at this time.

It should be noted that many of the “full-spectrum” and “wide-spectrum” tungsten filament incandescent lamps currently on the market produce no ultraviolet-B radiation (Gehrmann, 1992) or very low levels of ultraviolet-B radiation (Gehrmann, 1996). These lights are useful for providing visible light and heat, but their modest output of ultraviolet light, either ultraviolet-A or ultraviolet-B radiation, makes their role in vitamin D biogenesis questionable. A radiometer that measures ultraviolet-B emission and one that measures ultraviolet-A emission is currently available in the pet trade, but is somewhat expensive (ZooMed, San Luis Obispo, CA). These radiometers may not separate out the biologically relevant wavelengths within the categories, and are different from those used to report ultraviolet emission of commercially available bulbs (Gehrmann, 1996). Other radiometers are commercially available that can help identify the suitability of bulbs (biological activity) as well as their useful lifespan.

Ultraviolet radiation does not transmit well through standard glass or plastic. There now are specialty plastics on the market that are designed specifically for ultraviolet light transmission, but they are expensive and not commonly available. This means that when lights are placed above an enclosure lid made from glass or plastic (including thin pliable sheet plastic), ultraviolet-B radiation is screened out. For this reason, lights should not be encased in a plastic shield, and they should only be located above a screened lid that allows direct penetration of light. Alternatively, uncovered fluorescent lights can be located inside the enclosure.

Recently, a low-lead glass aquarium cover was introduced into the marketplace that purports to allow ultraviolet light transmission. In fact, small amounts of ultraviolet-A radiation are transmitted through the glass, but little or no ultraviolet-B radiation (Messonnier, 1995).

The lighting needs of nocturnal amphibians are poorly known, but low-level lighting to replicate the cycle of the moon should be provided. At NAIB, light- emitting diode (LED) night-lights, placed directly above a cage lid, appear to produce adequate light for nocturnal anurans to hunt, and yet do not appear to interfere with other nighttime activity (e.g., male calling, breeding, feeding). Red light (15-watt incandescent lights behind a red filter), and “bright” (4- watt) white night-lights placed within several feet (less than 1 m) of an enclosure, appear to interfere with normal nocturnal behavior. The moonlight bulbs designed for marine aquariums may have some utility in the herpetoculture of nocturnal amphibians, but this remains to be studied.

In general, amphibians appear to prefer subdued lighting (basking in sunlight is a notable exception). The glare from lights over an amphibian enclosure can be reduced by putting a sheet of plastic egg-crate screening directly underneath the light fixture. This screening is sold in many hardware and lighting stores for use with fluorescent ceiling lights. It has a large, open square pattern that permits direct transmission of overhead light.

Although the enclosure lighting should first and foremost meet the needs of the amphibians, a secondary consideration must be the lighting requirements of the enclosed plants. By selecting plants that thrive in moderate to low light levels, planting the most light-demanding ones closest to the lights, and arranging plants to shade at least some of the areas frequented by the amphibians, it is possible to have a vivarium that meets the needs of both plants and animals. It should be noted that the incandescent and fluorescent lights sold specifically for growing indoor plants (e.g., Gro-Lux® and Gro-Lux/ws®, Sylvania Corporation, Danvers, MA) do not produce ultraviolet-B radiation (Gehrmann, 1994) and should not be used in place of full-spectrum fluorescent lighting in animal enclosures.

The photoperiod in the vivarium should be maintained in a cycle that mimics that found within the amphibian’s natural range. The United States Naval Observatory Web site (http://aa.usno.navy.mil/AA/ data/docs/RS_OneYear.html) provides a calculator to determine the time of sunrise and sunset anywhere in the world. Day length data is also available in the printed serial, Astronomical Almanac (Nautical Almanac Office, 1999).

It is recommended that the lights over an amphibian enclosure be arranged to turn on and off in sequence, to simulate dawn and dusk. Twilight transitions have been shown to have a significant effect in normalizing activity patterns of laboratory animals (Greenberg, 1992). While this research did not include amphibians, it is reasonable to assume that sighted amphibians may benefit from gradual rather than abrupt lighting changes, just as they occur in the wild.

Features of Amphibian Nutrition

Prior to metamorphosis, anurans may be herbivorous, omnivorous, or carnivorous, depending on the species. After metamorphosis, diets typically shift to being completely carnivorous, although there are a few exceptions. Larval and adult salamanders and caecilians are strictly carnivorous. (See also Chapter 6, Diets for Captive Amphibians.)

Prey type and size vary, depending on the life stage, size, and species of amphibian. The adult stage of some species specialize on tiny leaf litter insects. Larger species of amphibians tend to be opportunistic and prey on a variety of species ranging from arthropods to small vertebrates.

It is a misconception that wild animals are nutritionally wise and will always select a balanced diet if given a choice (Allen, 1989). A captive diet should not be based simply on what items an amphibian eats most readily. Keep in mind that selection of food in the wild depends on a number of factors, including seasonal shifts in composition and abundance of prey, the amphibian’s prior experience with a particular prey species, as well as prey attributes of size, movement (orientation and speed), palatability and nutritive value (Stebbins & Cohen, 1995). It is the responsibility of herpetoculturists to devise varied and balanced diets for their captive amphibians.

Captive weights and body outline should mimic wild weights and body appearance. It is especially important that amphibians be in good weight prior to any breeding attempt, as this is an energetically expensive undertaking, and in some species, a period of little or no food intake.

Overfeeding and obesity can be a problem for some species of amphibians in captivity (e.g., White’s treefrog, Pelodryas caerulea, ornate horned frog, Ceratophrys ornata, tiger salamander, Ambystoma tigrinum). The recommended frequency of feeding varies with the species, age, and activity level (which may be influenced by cage enrichment and environmental variables) of the amphibian. Young, growing animals, and active foragers thrive on daily feeding. Mature sit-and-wait predators (e.g., the horned frogs, Ceratophrys spp.) will usually maintain good body weight with a large meal every 2 weeks.

In general, larval amphibians should be fed small amounts daily, rather than several large meals weekly. For species prone to cannibalism, it is important to provide food ad libitum if the tadpoles are to be raised communally. It is recommended that feeding, as well as cleaning, be done on a variable time schedule. Larvae of the bullfrog, Rana catesbeiana, respond to a fixed schedule of disturbance (feeding and tank cleaning) by accumulation of coelomic fat and delayed metamorphosis (Culley, 1991; Horseman et al., 1976). The excess fat restricts the mobility of some froglets, leading to starvation and death in some instances. The studies concluded that the larvae must be disturbed on an irregular time schedule, from hatching through to metamorphosis, to prevent these problems.

Common invertebrate foods for postlarval terrestrial amphibians include red worms, earthworms, white worms, crickets, fly maggots and adults, fruit flies, springtails, mealworm larvae, waxmoth larvae, and Zophobas beetle larvae. Aquatic amphibians also accept invertebrates such as bloodworms, black worms, washed brine shrimp, Artemia spp., glass shrimp, and crayfish. Techniques for culturing live food are covered in Chapter 6, Diets for Captive Amphibians, as well as the following sources: Axelrod & Schultz, 1990; Brown, 1995; Culley, 1991; Frye 1991,1992; Masters, 1975; National Research Council, 1974. Additional sources with information on diets and care of some of the more commonly kept amphibians are: anurans (Cover et al., 1994; de Vosjoli, 1990a, 1990b; de Vosjoli et al. 1996; Fenolio & Ready, 1995; Le Berre, 1993) salamanders (Balsai, 1994; Fenolio & Ready, 1996; Harkavy, 1993; Jaeger, 1992; Maruska, 1994; Staniszewski, 1996; Webb, 1994), caecilians (O’Reilly et ah, 1995; Wake, 1994).

Field sweepings and leaf litter invertebrates from areas where pesticides and herbicides have not been used are excellent food sources for amphibians. As a precaution, though, brightly colored insects should be avoided unless they are positively known not to be toxic. Mosquito larvae are a good food for many larval salamanders as well as for some tadpoles. A bucket of water left outside in warm weather will often be seeded within a few days. Equipment for catching and keeping insects is available from Bio-Quip Products (17803 La Salle Ave, Gardena, CA).

The National Research Council (1974) notes that cooked spinach, a food commonly fed to many herbivorous tadpoles, should be avoided because it can cause kidney stones. Cooked romaine and escarole lettuces do not cause this problem, though their nutritional adequacy remains uncertain. At NAIB, the tadpoles of nearly all species of anurans are fed dried fish food. (Sera Micron: Stage 1 Powdered Food for Newborn Fry, Sera, Heinsburg, Germany). At NAIB, stream-dwelling larvae of the harlequin stubfoot toad, Atelopus v. varius, feed on Sera Micron, as well as algae that is cultured in-house on PVC pipe fittings and on rocks.

Refference: Allen, M.E. 1989. Nutritional Aspects of Insectivory. Ph.D. Dissertation, Michigan State University, East Lansing, MI, 205 pp.

Allen, M.E. and O.T. Oftedal. 1989. Dietary manipulation of the calcium content of feed crickets. Journal of Zoo and Wildlife Medicine 20(l):26-33.

Axelrod, H.R. and L.P. Schultz. 1990. Handbook of Tropical Aquarium Fishes. TFH Publications, Inc., Neptune City, NJ, 718 pp.

Baetjer, A.M. 1968. Role of Environmental Temperature and Humidity in Susceptibility to Disease. Arch Environ Health 16:565-570.

Balsai, M.J. 1994. Axolotls. Reptile and Amphibian Magazine (March/April):41-51.
Brown, L.E. 1995. Successful mealworm raising. Reptile 8c Amphibian Magazine (March/April):74-79.

Cardeilhac, P.T. and B.R. Whitaker. 1988. Copper treatments, uses and precautions. Veterinary Clinics of North America: Small Animal Practice 18(2):435—448.

Coburn, J. 1992. The Proper Care of Amphibians. TFH Publications, Inc., Neptune City, NJ, 256 pp.

Cover, J.F. Jr., S.L. Barnett, and R.L. Saunders. 1994. Captive management and breeding of dendrobatid and neotropical hylid frogs at the National Aquarium in Baltimore, in J.B. Murphy, K. Adler, and J.T. Collins (Eds.): Captive Management and Conservation of Amphibians and Reptiles. Society for the Study of Amphibians and Reptiles, St. Louis, MO, pp. 267-273.

Culley, D.D. 1991. Bufo culture, in C.E. Nash (Ed.): Production of Aquatic Animals, World Animal Science C4. Elsevier Science Publishers, British Vancouver, Canada, pp. 185-205.

de Vosjoli, P. 1990a. The General Care and Maintenance of Horned Frogs. Advanced Vivarium Systems, Lakeside, CA, 32 pp.

de Vosjoli, P. 1990b. The General Care and Maintenance of White’s Tree Frogs and White-lipped Tree Frogs. Advanced Vivarium Systems, Lakeside, CA, 28 pp.

de Vosjoli, P. 1995. Vivarium design. A tropical rainforest vivarium. The Vivarium 7(2): 14—16.

de Vosjoli, P., R. Mailloux, and D. Ready. 1996. Care and Breeding of Popular Tree Frogs. Advanced Vivarium Systems, Santee, CA.

Duellman, W.E. and L. Trueb. 1986. Biology of Amphibians. McGraw-Hill Book Co., New York, 670 pp.

Fenolio, D. and M. Ready. 1995. Phyllomedusine frogs of Latin America in the wild and in captivity. The Vivarium 5(6):26—37.

Fenolio, D. and M. Ready. 1996. California: the Ensatina State. The Vivarium 7(4):32-60.
Fogel, D. 1993. Heating Herps in the 1990s. The Vivarium 4(6):8-ll.
Frye, F.L. 1991. A Practical Guide for Feeding Captive Reptiles. Krieger Publishing Co., Malabar, FL, 171 pp.