The Japanese giant salamander (Andrias japonicus ) is a species of salamander in the family Cryptobranchidae. This fully aquatic salamander is endemic to Japan, where it is known as Ōsanshōuo (オオサンショウウオ/大山椒魚), literally meaning "giant salamander". Other local names include Hanzaki , Hanzake , and Ankou. With a length of up to 5 feet (1.5 m), it is the third-largest salamander in the world, only being surpassed by the very similar and closely related Chinese giant salamander (A. davidianus ) and South China giant salamander (A. sligoi ). There are currently only five known members of the family Cryptobranchidae: the Japanese, Chinese, and South China giant salamanders, an undescribed Andrias species from eastern China, and the hellbender (Cryptobranchus alleganiensis ) in the eastern United States.
The Japanese giant salamander was first catalogued by Europeans when the resident physician of Dejima Island in Nagasaki, Philipp Franz von Siebold, captured an individual and shipped it back to Leiden in the Netherlands, in the 1820s. The species was designated as a special natural monument in 1951, and is federally protected.
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NocturnalNocturnality is an animal behavior characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal",...
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CarnivoreA carnivore meaning 'meat eater' is an organism that derives its energy and nutrient requirements from a diet consisting mainly or exclusively of a...
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PiscivoresA piscivore is a carnivorous animal that eats primarily fish. Piscivorous is equivalent to the Greek-derived word ichthyophagous. Fish were the die...
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NatatorialNatatorial animals are those adapted for swimming. Some fish use their pectoral fins as the primary means of locomotion, sometimes termed labriform...
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TerritorialA territory is a sociographical area that which an animal consistently defends against the conspecific competition (or, occasionally, against anima...
Oviparous animals are female animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive...
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PolygynyPolygyny is a mating system in which one male lives and mates with multiple females but each female only mates with a single male.
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PolygamyPolygamy is the practice of breeding with multiple partners. When a male breeds with more than one female at the same time – it is called polygyny....
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Not a migrantAnimals that do not make seasonal movements and stay in their native home ranges all year round are called not migrants or residents.
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starts withThe Japanese giant salamander can grow to a length of 5 feet (1.5 m) and a weight of 55 pounds (25 kg). The largest wild specimen on record weighed 58 lb (26.3 kg) and was 4.46 ft (136 cm) long. It is the third-largest amphibian in the world, only smaller than its close relatives, the South China giant salamander and the Chinese giant salamander. The brown and black mottled skin of A. japonicus provides camouflage against the bottoms of streams and rivers. Its body surface is covered with numerous small warts with distinctive warts concentrating on its head. It has very small eyes with no eyelids and poor eye sight. Its mouth extends across the width of its head, and can open to the width of its body.
A. japonicus possesses large skin folds on its neck that effectively increase its overall body surface area. This assists in epidermal gas exchanges, which in turn regulates carbon dioxide and oxygen exchange with the water. Capillaries in the surface of the skin facilitate this gas exchange. The skin folds along each side of the body are more pronounced in the hellbender than in the Japanese giant salamander.
The Japanese giant salamander can be distinguished from the Chinese giant salamander by the arrangement of tubercles on the head and throat. The tubercles are larger and more numerous compared to the mostly single and irregularly scattered tubercles of the Chinese giant salamander. The snout is also more rounded, and the tail is slightly shorter.
Adult males develop enlarged cloacal glands during the breeding season. Compared to an adult female, an adult male typically possesses a larger and wider head in proportion to its body. It is difficult to distinguish sex outside of the breeding season.
The Japanese giant salamander occurs in southwestern Japan (west of Gifu Prefecture in Honshu and parts of Shikoku and Kyushu). In particular, Okayama, Hyogo, Shimane, Tottori, Yamaguchi, Mie, Ehime, Gifu, and Ōita Prefecture are known to harbor its robust populations. They are typically found in fast-flowing mountain streams of these prefectures. It has been speculated that some of the populations in Wakayama Prefecture were introduced by humans and it is unknown whether naturally-distributed populations exist in Wakayama Prefecture.
The Japanese giant salamander occurs in freshwater habitats ranging from relatively large river (20-50 m) to small headwater streams (0.5 - 4 m). Smaller breeding adults tend to use small headwater streams presumably in order to avoid intraspecific competition with larger individuals in larger streams. Mark-recapture records suggest that giant salamanders migrate between a mainstem and tributaries of the same river. Environmental DNA surveys and the following physical field surveys suggest that small headwater streams likely serve as important habitats for juveniles and larvae. While habitat degradation threatens the Japanese giant salamander, it can inhabit disturbed streams surrounded by agriculture fields such as rice paddy fields. Adults appear to do well in a stream surrounded by rice paddy fields because rice paddy fields provide habitats for frogs, which serve as primary diet for adult giant salamanders in such a stream. However, streams surrounded by rice paddy fields are typically characterized by agricultural dams and concrete stream banks, which likely imposes a negative impact on their reproduction and thus result in low recruitment.
The Japanese giant salamander is restricted to streams with clear, cool water. Due to its large size and lack of gills, it is confined to flowing water where oxygen is abundant. it is entirely aquatic and almost entirely nocturnal. Unlike typical pond-breeding salamanders whose juveniles migrate to land after losing their gills through metamorphosis, it stays in the aquatic habitat even after metamorphosis and breaches its head above the surface to obtain air without venturing out of the water and onto land. The salamander also absorbs oxygen through its skin, which has many folds to increase surface area.
When threatened, the Japanese giant salamander can excrete a strong-smelling, milky substance. It has very poor eyesight, and possesses special sensory cells covering its skin, running from head to toe, the lateral line system. These sensory cells' hair-like shapes detect minute vibrations in the environment, and are quite similar to the hair cells of the human inner ear. This feature is essential for hunting prey due to its poor eyesight.
Adults feed mainly on freshwater crabs, frogs, and fish. It has a very slow metabolism and can sometimes go for weeks without eating. It lacks natural competitors. It is a long-lived species, with the captive record being an individual that lived in the Natura Artis Magistra, the Netherlands, for 52 years. In the wild, it may live for nearly 80 years.
The Japanese giant salamander remains in bodies of water its entire life. During the mating season, typically in late August and early September, sexually mature males start actively finding suitable nesting sites and often migrate upstream into smaller sections of the river or its tributaries. Because of the limited availability of suitable nesting sites, only large and competitive males are able to occupy nesting sites and become den masters. A den master diligently cleans his den guards his den against intruders including other males who try to steal the den while allowing a sexually active female enter the den. Mating begins as the female starts laying eggs and the den master starts releasing sperm, which often stimulate other subordinate males hiding around the den to enter the den and join the mating. As a result, a single female often mates with multiple males. The den master stays in the den with the fertilized eggs while the other males and the female leave the den. He provides parental care for the embryos by guarding the eggs and fanning water over them with his tail to increase oxygen flow. The den-master continues providing parental care for the hatchlings until the following spring when the larvae start dispersing from the nest. Researchers also observed that den masters consumed eggs and larvae that showed the sign of failed fertilization, death, or water mold infection. The researchers termed the behavior of selectively eating his own eggs or larvae "hygienic filial cannibalism" and hypothesize that this behavior importantly increases the survivorship of the remaining offspring by preventing water mold infection on the dead offspring from spreading over the healthy offspring.
The Japanese giant salamander is threatened by pollution, habitat loss (among other changes, by the silting up of the rivers where it lives), dams and concrete banks, and invasive species. In particular, it is important to note that the construction of concrete streambanks and agricultural dams throughout the distribution range has imposed a significant negative impact on giant salamanders. Concrete banks have deprived of habitats suited for nesting sites, and dams block migration paths and have caused habitat fragmentation. With the ongoing climate change, it is predicted that frequency and intensity of rainstorms in Japan will increase. These rainstorms will likely destroy stream banks more frequently, which could result in the construction of more flood-control dams and concrete banks.
Introgressive hybridization between the native Japanese giant salamander and the introduced Chinese (or South China) giant salamander is one of the major conservation challenges. It has been suggested that although the details are not known, the Chinese giant salamanders imported for food to Japan in 1972 were the sources of the ongoing introgressive hybridization. In Kamo River in Kyoto Prefecture, the study conducted from 2011 to 2013 found that 95% of the captured giant salamanders were hybrids. The introgressive hybridization appears to be spreading across several watersheds.
In some regions, giant salamanders used to be hunted as a source of food, but hunting has ceased because of the protection acts established after World War II.
The Japanese giant salamander is considered Near Threatened by IUCN, and is included on CITES Appendix I. It is considered Vulnerable by the Japanese Ministry of the Environment. Additionally, it has been given the highest protection as a “Special Natural Monument” by the Japanese Agency for Cultural Affairs since 1952 due to its cultural and educational significance.
