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Amphibians as Laboratory Animals

By Brent R. Whitaker, MS, DVM, National Aquarium

Amphibians have long been used as laboratory animals. In an effort to enable scientific research while maintaining humane and ethical principles, the 8th edition of The Care and Use of Laboratory Animals (National Research Council, National Academies Press, 2011) provides organizations conducting research on animals, including aquatic animals, with information regarding environment, housing, management, and veterinary care. This guide should be consulted when using amphibians in research. (Also see Laboratory  Animals.) Species that are captive born and readily available from commercial suppliers include the African clawed frog (Xenopus laevis, X tropicalis), the African dwarf frog (Hymenochirus boettgeri), the fire-bellied toad (Bombina orientalis), the axolotl (Ambystoma mexicanum), and the tiger salamander (A tigrinum). Wild-caught species collected by researchers or vendors for use in the laboratory include the northern leopard frog (Rana pipiens, sometimes called the grass frog), bullfrog (R catesbeiana), cane toad (Bufo marinus, sometimes called the marine toad), and the mud puppy (Necturus maculosus). Other North American ranid frogs are sometimes used. When collecting or importing amphibians, it is important to abide by state laws and obtain all required permits.

Pelleted diets are available for some aquatic species, like African clawed frogs, bullfrogs, and axolotls, making it easier to feed large groups. These foods must be stored in a cool, dry location to maintain freshness. Uneaten food should be removed after all animals appear satiated to avoid fouling the tank. Handling and research protocols should be developed to minimize stress to the animals. Overcrowding must be avoided to maintain sanitation, prevent disease transfer, and reduce social stress.

Most aquatic species used for laboratory studies are kept in large, recirculating systems that have multiple tanks using a common water supply. Water is filtered, sent to individual tanks, and then returned for filtration and disinfection. Proper water quality is maintained using one or more types of filtration. These include a mechanical filter to remove suspended waste material, a biofilter to convert nitrogenous wastes to less toxic compounds, and a chemical filter to remove dissolved organic compounds. The addition of an ultraviolet sterilizer to inactivate microorganisms is highly recommended. Bulbs must be kept clean and changed every 6–8 mo for the ultraviolet sterilizer to remain effective. Ozone, a potent oxidant, may also be used with caution to remove suspended organic material and potential pathogens from the water.

Ammonia toxicosis is common in systems that have not established a good biofilter. Amphibians exposed to inappropriate levels of ammonia typically produce excess mucus, become dull in color, and attempt to escape. Amphibians should be removed from the contaminated water and rinsed thoroughly with dechlorinated and well oxygenated fresh water. A diagnosis can be confirmed if the source water has ammonia at levels >0.5 ppm, although toxicity can be seen at levels >0.1 ppm for some species. Many tropical fish stores sell test kits that check for ammonia.