Japanese Giant Salamander

## Description

The ***Japanese Giant Salamander*** (***Andrias japonicus***) is a heavily built salamander, and with its Chinese sister species, the *japanese giant salamander*, is one of the two largest extant salamander species. Head broad and flat. Body strongly depressed; terminal two-thirds of tail strongly compressed; nostrils small, near tip of the snout, their distance from each other less than one-half the distance between the eyes, which are without eyelids and very small. Vomerine teeth in an arched series starting between the choanae, parallel to the maxillary and premaxillary series. Thin lower labial fold starting midway between nostril and eye to angle of mouth. Legs short and flattened. Tail short, slightly more than one-third the length of head and body, with a high dorsal fin beginning at insertion of hind legs, and a lower ventral fin. Skin rather smooth and slippery, with wrinkles, folds and tubercles.

No external sexual dimorphism. During the breeding season, cloacal lips are swollen in the male and flat in the female.

The salamander's color is usually reddish-brown to brownish-yellow, paler below; irregularly blotched and marbled with dusky spots. Considerable individual variation ranging from being completely black to almost yellow.

Total length of an adult *japanese giant salamander* ranges from 30 to 150 cm - with a snout vent length of 20 to 90 cm - a result of continuous growth after sexual maturity (Kawamichi and Ueda 1998). Many specimens found in the wild are 60-70 cm (Environment Agency of Japan 2000). Weight of sexually mature animals ranging between 1.5 and 35 kg. The heaviest specimen found in the wild, on record, was 26.3 kg and measured 136 cm (Tochimoto, pers. com). Genetic variation is low (Matsui and Hayashi 1992, Matsui et al. 2008).

The *Japanese Giant Salamander* is closely related and very similar to the Chinese Giant Salamander (*A. davidianus*) and differs from the latter by the arrangement of tubercles on the head and throat. These tubercles are larger and more numerous than in *A. davidianus*; they are mostly single and irregularly scattered. The snout is more rounded and the tail a little shorter in the Japanese species.

## Distribution and Habitat

The *japanese giant salamander* is endemic to Japan, where it is found in the Chubu, Kinki and Chugoku regions of central and western Honshu, in Shikoku and in northeastern Kyushu (Tochimoto 1996).

The salamander occurs in habitats ranging from relatively large rivers (20-50 m wide) to small tributary streams (1-4 m wide), with clear cool water flowing through granite and schist regions. These streams have usually rocky or gravel bottoms, and at places shallow, quietly running water. The animals keep themselves concealed in rocky caverns or in burrows on the water’s edge (Tago 1927). Vertical distribution 300 to 1000 m. Spawning nests and larvae often occur in relatively small lotic habitats, including the upper reaches of tributary streams (Okada et al. 2008).

## Life History and Special Behavior

Spawning occurs in late August to early September. Eggs are deposited in long strings, containing 400-600 eggs. Diameter of egg 5 mm; diameter of external gelatinous capsule 8 to 15 mm. At water temperatures between 8° and 18° C embryonic development takes 40 to 60 days (Kuwabara et al. 1989). Larvae hatch in October-November at a total length of 30 mm and start feeding after absorption of yolk. One year old larvae measure about 100 mm, three year olds some 200 mm. At this size larvae start losing their gills. Males reach sexual maturity at 30 cm, females at 40 cm. The larval period is about 4-5 years, and it takes another 10 years to reach adulthood (Ministry of the Environment, Japan 2008).

The salamanders are entirely aquatic and nocturnal. They feed on fresh-water crabs, fish, small amphibians (Tago 1927), and additionally on aquatic insects and small mammals (Goris and Maeda 2005). Males and females have overlapping home ranges and are more or less sedentary outside the spawning period. During the breeding season, in August-September, both sexes congregate at underwater nest sites, consisting of 100 to 150 cm long burrows into or near the river bank. Nests have a single entrance opening underwater. Favorable nest sites may be used during successive years. Both males and females may occupy more than one nest at the time, with large and heavy males ("den-masters") attempting to monopolize occupancy of the nest sites. Nests are guarded from inside by males, attacking other males who try to enter. Males may also patrol around the nest area, chasing and attacking other males. Females enter the nests more than once and lay their eggs in the cavity, where they are fertilized by the male. At this stage several other males may intrude and try to fertilize the eggs. After spawning, den-masters remain at the nests for more than one month and aggressively guard the eggs until hatching occurs or until late October. Dominance rank of den-masters among males attempting to breed appears to be strong. Dead and heavily injured males have often been found during September (Kawamichi and Ueda 1998).

Thanks to new field studies of *A. japonicas*, we now know that males provide parental care, and for a very long period of time. Males actively seek burrows in stream banks that might serve as sites for mating and nesting. Females enter the burrow, occupied by a "den master" male and mating and external fertilization of the eggs takes place. The den master then provides parental care (tail fanning, agitation of eggs, and hygienic filial cannibalism of unfertilized eggs, or dead or dying embryos and larvae and other specialized behaviors) (Takahashi et al. 2016). Such behavior occurs over a long time period, up to seven months. The study adds substantial new information concerning egg deposition and parental care in nature, and will be critical for attempts to improve habitat and other recovery attempts for these amazing animals.