proportion to its body. It is difficult to distinguish sex outside of the breeding season. Distribution 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. Behavior 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