Chapter 10 Amphibians
|Horned frogs (Ceratophrys spp)||From South America, these sit-and-wait predatory frogs grow large and have a strong bite||Aeromonas infections, gout, corneal lipidosis|
|Poison-arrow frogs (Dendrobates spp)||South American. Skin toxins are based on plant alkaloids ingested by native prey insects. Captive bred and long-term captives usually safe to handle with appropriate precautions||Bacterial and fungal infections|
|White’s tree frogs Littoria caerulea||A large Australian tree frog requiring high temperatures (26–32°C daytime; 20–24°C nighttime) and a comparatively low humidity (50–60%)||Bacterial and fungal infections|
|African clawed toad Xenopus laevis (in both wild and albino forms)||Totally aquatic. Extremely popular||Bacterial and fungal infections. Poor water quality|
|Axolotl Ambystoma mexicanum||A neotenous salamander originating from Mexico. Keep cool (15–20°C)||Poor water quality, ingestion of foreign bodies, bite injuries from other axolotls|
|Caecilians, such as Typhlonectes compressicauda||These aquatic and moist subterranean worm-like amphibia are occasionally available in aquarium outlets||Fungal skin infections, poor water quality|
Handle amphibians with damp hands and/or smooth latex gloves to protect the delicate skin and mucous covering. Amphibia can be very unpredictable and are excellent at leaping from the unsuspecting grasp of the veterinarian, therefore beware of potentially traumatic falls to the floor. Wrapping them in very damp, thin paper towels enables some control; areas of interest are accessed by gently tearing through the paper.
Large frogs such as horned frogs (Ceratophrys spp) and African giant frogs (Pyxicephalus adspersus) can inflict a painful bite and are likely to do so. Handle these by gently grasping them around the waist. Large marine toads (Bufo marinus) may eject toxins from their parotid glands if severely stressed. Wild-caught poison-arrow frogs can produce potentially very toxic skin secretions which are manufactured from prey; captive-bred frogs usually do not produce such toxins but caution is advised.
Most amphibia have very thin, moist skins, which allow significant absorption of topical medications. This should be borne in mind if using topical preparations designed for mammalian species but these can be used advantageously, as therapeutic levels of active medications may be able to be achieved following topical application of injectable drugs, e.g. antibiotics.
Dehydrated amphibians show increased tackiness of the skin mucous covering, tightening of the skin, sunken eyes and weight loss. Dehydration can also affect cutaneous gaseous exchange leading to hypercapnia and acidosis.
Terrestrial amphibians have several respiratory surfaces, which can complicate the control of anaesthesia. These include the lungs, skin and buccal lining. Aquatic amphibia respire largely through gills.
When inducing terrestrial amphibia in a water bath always guard against the possibility of drowning. Once anaesthetized, large amphibia can be intubated and maintained as for reptiles with isoflurane, but maintenance can be difficult due to alternative respiratory surfaces.
The amphibian skin is thin and covered with a layer of mucous, which acts as an antibacterial and antifungal barrier. It is highly porous to medications and toxins; many treatments can be administered topically to achieve systemic effects. Normal flora are G −ve, such as Aeromonas spp, Pseudomonas spp, Proteus spp and E. coli. However, these can also be pathogenic and so results may require a degree of interpretation.
Amphibians respire through a variety of organs – namely the lungs, buccopharyngeal lining, skin and gills (larval amphibia). In terrestrial amphibia dehydration may affect gaseous exchange at the skin leading to hypercapnia and acidosis.