Diets for Captive Amphibians. Adult Aquatic Amphibians

Invertebrates make up the bulk of the natural diet of most species of aquatic amphibians, whether they are frogs, salamanders, or caecilians, and generally they accept very similar diets in captivity. There are some species of aquatic amphibians that are specialists and feed on only one or a few types of prey in the wild, but many of these adapt to a different diet in captivity. Some species of aquatic caecilians, such as the Cayenne caecilian, Typblonectes compressicauda, have been kept and bred over multiple generations on a diet consisting primarily of earthworms.

Aquatic salamanders such as the axolotl, Ambystoma mexi- canum, and the red-spotted newt, Notophthabnus viridescens, generally accept whole or chopped annelid worms as well as other whole or chopped invertebrates. Earthworms, Lumbricus spp., bloodworms (midge larvae, family Chironomidae), black worms, Lumbriculus variegatus, tubifex worms, Tubifex tubifex, white worms, Enchytraeus spp., glassworms, washed brine shrimp, Artemia salina, water fleas, Daphnia spp. and Cyclops spp., grass shrimp, Palaemonetes spp., crayfish, springtails, Collembola spp., flour beetles and larvae, Tribolium confusum, newly molted mealworm larvae, Tenebrio molitor, crickets, wax worms (larvae of either Galleria mellonella or Achroia grisella) and fly larvae and wingless adult flies (Musca spp. or Drosophila spp.) are commercially available invertebrates that can be used as elements of the diet for captive salamanders. Feeder fish (e.g., guppy, platy, goldfish, and loach) can be offered to the larger aquatic amphibians, as can many of the smaller freshwater fish, such as whole smelt.

Live moving prey is accepted more eagerly than dead stationary prey, but most aquatic amphibians will learn to accept dead prey. Many caecilians, salamanders, and frogs will learn to accept food offered on forceps or impaled on the tip of a broom straw, while others remain timid and reluctant to feed in the presence of humans. An amphibian that learns to accept dead prey is easily fed, since frozen invertebrates and vertebrates are packaged and sold as fish food and are readily available at most pet stores that sell fish and fish supplies. A change in appetite, either gradual or sudden, is often the first clue to an amphibian’s health, so hand feeding is encouraged for it allows the caregiver to keep track of the amphibian’s appetite.

Live food is also available through most pet and bait stores, but may only be available seasonally. The clinician is advised to determine local sources for these food items so that the client can quickly acquire food when the need arises. These commercially available prey items can be supplemented with invertebrates that can be collected in the field. Small insects, sometimes referred to as meadow plankton, can be harvested with a sweep net brushed through tall grasses and light shrubs. Slugs, small grasshoppers, mosquito larvae, and other invertebrates are relished by many aquatic amphibians. Wild-collected food items are not without hazards however, for these items may be contaminated with pesticides and other harmful compounds and may be an intermediate host for parasites affecting amphibians. Mosquito larvae and other aquatic invertebrates can be collected from natural water sources, but may serve as a vector for infectious diseases.

Care should be taken to screen aquatic prey items to avoid introducing pathogens such as ectoparasitic protozoa. A 10- or 20-gallon glass tank can be used for quarantine holding of live food items, and a program to remove parasites instituted. A safe and simple treatment to reduce the numbers of ectoparasites on aquatic invertebrates is immersion in a saltwater bath (25 g sea salt/L water). Different species of invertebrates can tolerate different lengths of time immersed in a salt bath, and should be monitored for signs of distress to a maximum time of 60 minutes. Fish can be treated similarly using either sea salts or a formaldehyde treatment (0.4 ml 37% formaldehyde/L water) can be used. All prey items should be thoroughly rinsed with fresh water following treatment, and allowed several hours in the quarantine tank before being used as amphibian food. Prophylaxis of bacterial disease may lead to the development of resistant strains of pathogenic bacteria and is not recommended for food items. If the items were collected from an unsanitary area or raised in an unsanitary manner, they should not be used as a food source for amphibians. Equal care should be given to screening frozen fish offered to amphibians, for Aeromonas salmonicida was introduced into a colony of the African clawed frog, Xenopus laevis, through contaminated food fish (Frye, 1989).

Some aquatic frogs and salamanders may learn to eat pelleted foods, displaying an individual preference for either floating or sinking pellets. It is important to remember that many of the fish foods are geared toward omnivorous fish and are not designed to be used as a diet for carnivorous vertebrates. Even the pelleted turtle diets are geared toward an omnivore rather than a strict carnivore. These omnivore diets may not meet the protein, fat, and fat-soluble vitamin needs of the carnivorous adult salamander or frog. Amphibians that receive a large portion of their calories from artificial diets may develop a variety of health problems, such as hydrocoelom from protein deficiency and skin lesions from fat deficiencies. Depending on the levels of fat and fat soluble vitamins in the food, disease from either vitamin D deficiency or toxicity might develop.