Andrias japonicus

Andrias japonicus is native to the northern region of Kyushu Island and western Honshu island of Japan. ("Smithsonian National Zoological Park", 2003)

Andrias japonicus is found at elevations between 180 and 1,350 meters. These salamanders reside in and around the cold, swift, mountain streams of the Japanese islands. These waters provide enough oxygen to diffuse through the epidermis of A. japonicus, facilitating an aquatic lifestyle. As with other cryptobranchid salamanders, A. japonicus tends not to leave the water and is thus particularly sensitive to receding mountain streams. ("Arkive--Images of Life", 2004; Gadow, 1901; Semlitsch, 2003)

Giant Japanese salamanders (Andrias japonicus) grow to approximately 1.5 meters in length and can weigh up to 25 kg. The long body of A. japonicus is covered with a wrinkled grey, black, and green epidermis that provides camoflauge. The tail is long and wide, and there are two pairs of legs, which are close in size. Andrias japonicus is endowed with minimal vision. Small, lidless eyes sit on the top of the wide, flat head. Gas exchange occurs through the epidermis. The wrinkles of the warty epidermis provide increased surface area, facilitating the exchange of carbon dioxide and oxygen with the water. Capillaries run close to the surfaces of the skin, allowing for the easy diffusion of gases.

The slow metabolism of Japanese salamanders allows these amphibians to live without consuming food for weeks at a time. Giant Japanese salamanders differ from other closely related species in that these particular salamanders lack gill openings and also have unique modifications with their branchial structures. ("Arkive--Images of Life", 2004; Gadow, 1901; Parker, 2001; Pough, et al., 2001)

Andrias japonicus grows continously throughout life. As with other amphibians, A. japonicus undergoes three developmental stages, including egg, larva, and adult forms. Hatching occurs 12 to 15 weeks after fertilization. Eggs usually measure 6 mm by 4 mm, and are mostly yellow in color.

Metamorphosis in this species is incomplete. Adults do not develop eyelids, and retain a single pair of closed gill slits on the neck. Andrias japonicus retains its larval teeth for life, and has lungs which are vestigial, performing no gas exchange. ("Arkive--Images of Life", 2004; Gadow, 1901; Parker, 2001; Pough, et al., 2001; Sleeper, 1997; Zug, et al., 2001)

Andrias japonicus begins the reproductive process in early autumn. In late August, the salamanders congregate at nesting sites, or spawning pits, which simply consist of rocky caverns, burrows, or hollowed impressions within the sandy streambed. Males aggressively compete to occupy these spawning pits. Once males have secured the nesting sites, females enter the nesting site to begin the fertilization process. Females approach males and proceed to make a spin-like motion. The female then releases her eggs within the spawning pit while the male fertilizes them. More than one female may release eggs into the same spawning pit. Males guard the eggs in the spawning pits until they hatch, 12 to 15 weeks after fertilization. This protects the eggs from other male salamanders and possible predators such as fish. Males ferociously defend and occupy a particular spawning pit for many years. Smaller males have been killed and eaten by larger males during the reproductive season. ("Arkive--Images of Life", 2004; Pough, et al., 2001; Sleeper, 1997)

Females release 400 to 500 eggs in the spawning pit protected by a male. These eggs are held together with a string-like substance and resemble threaded beads on a string. Fertilization is external. Eggs hatch 12 to 15 weeks after fertilization. The age at sexual maturity for A. japonicus is not known, although given male competition, it is likely that at least for males, successful breeding requires a large size. ("Arkive--Images of Life", 2004; Sleeper, 1997)

The exact amount of parental investment found in A. japonicus has not been thoroughly investigated. Females provision eggs with large quantities of nutrients, ensuring their survival. Males may contribute to the survival of the young through their protection of spawning pits. A male protects his spawning pit from predatory fish and other male A. japonicus. Males tend to protect these spawning pits until the eggs have hatched, 12 to 15 weeks after fertilization. ("Arkive--Images of Life", 2004; Pough, et al., 2001)

Giant Japanese salamanders can live for over fifty years. However, it is unlikely that most individuals live this long. Large numbers of offspring are produced each season, so mortality early in life is probably high. (Sleeper, 1997)

Andrias japonicus is nocturnal, usually sleeping underneath stream rocks during daylight hours. These salamanders are natatorial and motile. For normal movement, Giant Japanese salamanders walk on the bottoms of streams whereas an undulating type of movement is used to quickly travel short distances. Andrias japonicus uses a side-to-side movement to keep water circulating near the epidermis, so that deoxygenated water moves away from the skin, and oxygen-rich water replaces it. ("Arkive--Images of Life", 2004; Gadow, 1901; Zug, et al., 2001)

Andrias japonicus is territorial, with large males often killing smaller rivals in defense of spawning pits. Apparently as a means of defnese, A. japonicus expells a secretion that smells like the Japan pepper plant. This expulsion quickly hardens to a gelatinous substance in the open air. Although its function underwater is not understood, it may protect the individual expelling it. (Gadow, 1901; Pough, et al., 2001)

The home range for A. japonicus has not been reported.

With small eyes that provide little visual acuity, these nocturnal amphibians use the senses of smell and touch to perceive their environments. Little is known about the communication methods of A. japonicus. Tactile communication is apparently important between rival males, as well as between a male and female during breeding. The "smelly" expulsion produced under threat suggests that chemical communication may have some role in this species. The role of auditory cues in communication is unknown. ("Arkive--Images of Life", 2004)

Andrias japonicus is a carnivorous dietary generalist which engulfs prey by quickly opening and closing its warty mouth while sucking. By creating negative pressure within the mouth, A. japonicus produces asymmetrical suction. Assuming that A. japonicus follows the same suction habits as other cryptobranchid salamanders that suck asymmetrically, Giant Japanese salamanders drop one side of their jaw 10 to 40 degrees in order to suck in their prey. Because these salamanders feed in water, saliva is not needed.

These salamanders are known to consume:

Fish (Class Osteichthyes).

Insects (Class Insecta).

Crustaceans (Subphylum Crustarea).

Giant Japanese salamanders also eat worms, although details on the types of worms consumed are not available. ("Natural History Museum", 2005; Pough, et al., 2001; Sleeper, 1997)

Fish (Class Osteichthyes) are a main predator of A. japonicus eggs.

Humans have also used these salamanders as a source of food. They may still be used some traditional medicinal practices.

The long bodies of A. japonicus are covered with a wrinkled grey, black, and green epidermis in the adult stage that allows them to blend into the surrounding area and avoid potential predators. ("Arkive--Images of Life", 2004; "Smithsonian National Zoological Park", 2003)

Andrias japonicus serves as host for parasites. Studies have shown that giant Japanese salamanders can house parasitic roundworms, specifically Spiroxys hanzaki. (Hasegawa, et al., 1998)

Andrias japonicus is occasionally hunted and is sold for profit in Asia as a delicacy. There are reports that this species may be used in some traditional medicines. ("Arkive--Images of Life", 2004)

Local fishermen of the Japanese islands claim that A. japonicus consumes small sweetfish that inhabit the same mountain streams. Many locals fear that their fishing economy is damaged by the salamanders predation of small fish. (Parker, 2001)

The IUCN Red List of Threatened Species lists A. japonicus as a near threatened or lower risk species.

The first living specimen of A. japonicus that was captured and brought to a Western nation was found by von Siebold in 1829. Von Siebold is credited with the discovery of this species. This particular A. japonicus lived at least 52 years in captivity. (Gadow, 1901)