This family of primitive looking salamanders is named after the wrong assumption that the lack of visible gill slits meant that they must be hidden (their name means hidden gills in Greek). These are very large salamanders with the largest one, the Andrias davidianus, reaching 180 cm in length and 59 kg in weight, making it the largest living amphibian. The Cryptobranchidae closest sister group is the Hynobiidae, with which they share various characteristics, and the Cryptobranchidae are thought to have derived from hynobiid-like ancestors which retained larval characteristics in adults. They are characterized by large, robust and flattened head and body, small eyes, thick legs with stubby digits, lateral folds of skin and a later line, which allows them to sense prey movements in the water. The lateral folds of skin are an adaptation that increases skin surface, as these animals absorb most of their oxygen through their skin. The member of this family are also able to vocalise, with the common Chinese name of the Andrias davidianus being wawayu, which means baby fish, name they earned from their vocalisations which resembles a baby’s cry.
The family is composed by three species divided into two genera:
- Andrias: formed by two Asiatic species, the Chinese and Japanese Giant Salamanders
- Cryptobranchus: formed by one specie in North America
This family used to be more widespread and it contained more species that are now extinct, the most famous of which is the Andrias scheuchzeri. A fossil of this specie was discovered in Germany in 1726, and it was thought to be a human fossil from the biblical flood, until it was correctly identified as a salamander. The genus name Andrias is a homage to this first discovery, and it means “image of man”. Interestingly, the Andrias davidianus, discovered more than a century later, is not distinguishable from the fossil remains of Andrias scheuchzeri as the specie have changed very little with time, making some people believe that they are the same animal.
The species of this family are strictly nocturnal and feed on a variety of preys by a mechanism called “suction feeding”. By opening their mouth, they create an area of lower pressure, which forces water, and the preys, inside their mouth.
The breeding behaviour of the Andrias has been well documented, and it largely consists in the dominating male of an area defending a burrow where multiple females lay their eggs. Fertilisation is external, like with the Hynobiidae, and the dominant male, often referred to as Den-Master, fiercely protects the den from other males, fighting other males or even eating them if size allows it. This territoriality is well documented by an increase of injuries observed in males during the breeding season, but despite this, males of the Japanese Giant Salamander (Andrias japonicus) have been observed allowing smaller males into the nest. This behaviour is still not fully understood, but in Andrias japonicus, it has been observed that the den master may allow smaller males to enter the burrow, but only when a female is entering the burrow as well. Once the female is inside, and laying eggs, the smaller male is allowed to fertilise the eggs together with the dominant male, but it is then pushed away once the den master resumes protection of the eggs. The eggs are large, measuring 20-25 mm in diameter, linked together similarly to a string of beads, and take roughly 52-56 days to hatch. Once hatched the larvae measure around 3 cm in length and it takes 30-90 days for the yolk to be fully absorbed and for the larvae to start eating (30 days was achieved in artificial condition, while 90 days is achieved in a more natural settings). The larva take a year to reach 10 cm in length. After 3 years, they reach 20 cm and loose the gills, even though their branchial slits are still open. The larva fully complete metamorphosis around the 4 years mark, and at a size of roughly 26 cm. One of the captive breed Andrias japonicus from the Asa Zoological Park measured 42cm after 9 years.
The Andrias davidianus has also been the focus of several studies focused on increasing protection for this specie, but this specie face a unique challenge among salamanders. The specie is currently being bred in several farms located in their natural habitat, with the purpose of their meat being used for human consumption. The presence of these farms poses an interesting challenge from a conservation standpoint. On one side, there have been successful studies on the possibility to use stock from these farms for reintroductions in the wild of these animals, but on the other side, the farm environment increases the spread of illnesses. Another downside is that the animals in the farms do not have a unique origin, with farms often trading animals and mixing animals from different areas of China. Recent studies on the genetics of the Andrias davidianus have pushed the idea that the status of this specie may need to be revised, and the species split in 5-6 different species. This animal is after all bound to their aquatic habitat, meaning that populations in different rivers and area of China would not be able to interact, giving enough time for the formation of different species. As the animals in farms come from different rivers and area of China, the reintroduction of animals from farms would only be possible in cases in which the animals being reintroduces are not a mix of different localities.
Genus Andrias (2 species)
Genus Cryptobranchus (1 species)
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