Cave salamander  (Proteus anguinus)

Classified as Vulnerable (VU) on the IUCN Red List (1).

The cave salamander is a rare amphibian with an unusual appearance, shaped by several million years of living in dark, subterranean caves in central Europe (2). Its skin lacks pigment, giving its body a white, pasty appearance. It also has a pink hue due to blood capillaries near the skin, and as its translucency shows the contours of the internal organs. This strange fleshy skin led to this species' common name, the human fish, as people thought this bizarre amphibian resembled a small human (3). This cave dwelling amphibian's four limbs are short and feeble, and its eyes are so poorly developed that it is blind (2). Its head is elongated with a round snout, and on each side of the head there are three distinctive scarlet gill tufts that are used in respiration, although adults develop lungs as well (2). Males are smaller than females, and can be distinguished from females during breeding season by their larger cloaca (3).

Found in Bosnia and Herzegovina, Croatia, France, Italy and Slovenia (1).

The cave salamander inhabits underground fresh and well-oxygenated water systems in karst formations, where the water temperature is cool (between 6ºC and 12ºC) (3).

Little is known about the biology of this amphibian as it lives in caves and is difficult to study. Most observations are therefore from captive specimens. It feeds on insect larvae, molluscs and amphipod crustaceans, detecting its prey in total darkness by using chemical cues in the water (3).

Most males establish a territory during the breeding season, and furiously protect them from other males (3). When a female enters the territory, courtship begins. The male deposits a spermatophore, which the female picks up with her cloaca. Courtship can be repeated several times within a few hours, and the fertilized eggs are held inside the female's body (3). These eggs, 12 to 70 in number, may be deposited beneath a stone, and guarded by the male and female until they hatch. Alternatively, just one or two eggs may develop inside the female, the rest breaking down to provide nutrients for the female and the remaining developing offspring. In this case the female eventually gives birth to well-developed larvae (2). There is no clear metamorphosis and the adult maintains many juvenile characteristics throughout its life such as gills. Cave salamanders reach sexual maturity after seven years, and are estimated to live for up to 58 years (3).

The cave salamander is dependent on large aquatic cave systems. Tourism, economic changes and industrial pollution are the main threats to this species as the caves are affected by the land-use above. Its populations are also under pressure from collectors for the aquarist trade (3).

This species is becoming increasingly rare and, as individuals are removed from natural populations by collectors or for research, their ability to recover is reduced (2). This species must be more strictly protected by law, and breeding programs established to enable its survival (2).

For more information on cave salamanders and other amphibians see:

• Halliday, T. and Adler, K. (2002) The New Encyclopedia of Reptiles and Amphibians. Oxford University Press, Oxford.

• AmphibiaWeb:
  http://amphibiaweb.org//index.html

• Capillaries: small blood vessels that form an intricate network throughout the body for the interchange of various substances, such as oxygen and carbon dioxide, between blood and tissue cells.
• Cloaca: a common opening into which the reproductive, alimentary and urinary systems open.
• Crustaceans: diverse group of arthropods (a phylum of animals with jointed limbs and a hard chitinous exoskeleton) characterised by the possession of two pairs of antennae, one pair of mandibles (parts of the mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, slaters, woodlice and barnacles.
• Karst formations: areas of irregular limestone in which erosion has produced sinkholes, underground streams, and caverns.
• Larvae: stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
• Metamorphosis: an abrupt physical change from the larval to the adult form.
• Spermatophore: gelatinous jelly cone with a sperm cap deposited by a male during courtship and picked up by the cloacal lips of the female.
• Subterranean: living underground, in caves or groundwater.

1. IUCN Red List (May, 2009)
   http://www.iucnredlist.org
2. Halliday, T. and Adler, K. (2002) The New Encyclopedia of Reptiles and Amphibians.Oxford University Press, Oxford.
3. AmphibiaWeb (November, 2003)
   http://amphibiaweb.org//index.html