AmphibiaWeb - Hynobius retardatus
Hynobius retardatus
Hokkaido Salamander, Ezo Sansho-uo
Subgenus: Satobius
family: Hynobiidae
subfamily: Hynobiinae
Species Description: Dunn, E. R. 1923. New species of Hynobius from Japan. Proceedings of the California Academy of Sciences, 4th Series 12: 27–29.

© 2016 Henk Wallays (1 of 90)
Conservation Status (definitions)
IUCN (Red List) Status Least Concern (LC)
National Status None
Regional Status None
Access Conservation Needs Assessment Report.



View distribution map in BerkeleyMapper.
View Bd and Bsal data (1 records).

Hynobius retardatus has a snout to vent length of 60-85 mm and a total length of 115-200 mm. It has 11 costal grooves and its hindfeet have 5 toes. Its color is generally a patternless dark brown, but juveniles are liberally sprinkled with gold flecks. This gold speckling is also seen in the adults in many locations (Goris and Maeda 2004).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Japan


View distribution map in BerkeleyMapper.
View Bd and Bsal data (1 records).
Hynobius retardatus occurs from lowland to alpine zones in forests and grassland (IUCN 2006). [3719] It is found widely throughout Hokkaido, with the exception of the outlying islands. It is not found elsewhere (Goris and Maeda 2004).

Life History, Abundance, Activity, and Special Behaviors

Hynobius retardatus belongs to the family Hynobiidae, which is one of only two salamander families exhibiting external fertilization of eggs. This species is one of several where the males take part in a "scramble competition" for females (Hasumi 1994)[3756]. H. retardatus breeds from April to May in the lowlands, but may breed as late as July at higher altitudes. Breeding takes place mainly in still waters of permanent ponds or temporary puddles, but a small percentage of H. retardatus also breed in running water. When spring thaw begins, males leave their hibernacula and make their way to the breeding site. There they position themselves on twigs or other vegetation just below the surface of the water to wait for females. When a female arrives, she swims up to the twig, attaches one end of the egg sac to it, then releases her hold. A nearby male approaches and pushes her cloacal region with his hind legs while pulling out the egg sac with his forefeet. He is quickly joined in this by other males. Once freed of the egg sac, the female floats to the bottom and hides. The males fight over the egg sac, embracing it and ejecting sperm, so that the eggs are fertilized by many males (Goris and Maeda 2004). During the breeding phase, males also undergo a noticeable increase in head width (Hasumi and Iwasawa 1990; Hasumi 1994).

The egg sac generally forms a shapeless, transparent mass, although in some localities it is opaque. One clutch contains 60-150 eggs, which may hatch in 30-40 days. The larvae metamorphose 40-50 days later. In very cold regions, however, 2-3 years may elapse between egg laying and metamorphosis. The larvae often feed on the tadpoles of Rana pirica, and cannibalism is not uncommon when other prey items are scarce. Little is known of the habits of the juveniles and adults outside the breeding season (Goris and Maeda 2004).

The name "Yezo Salamander" has also been used in the literature. "Ezo" (or "Yezo," the old pronunciation of Ezo) is a historical name for the island of Hokkaido (Goris and Maeda 2004). [3684]


Goris, R.C. and Maeda, N. (2004). Guide to the Amphibians and Reptiles of Japan. Krieger Publishing Company, Malabar, Florida.

Hasumi, M. (1994). ''Reproductive behavior of the salamander Hynobius nigrescens: monopoly of egg sacs during scramble competition.'' Journal of Herpetology, 28(2), 264-267.

Hasumi, M. and Iwasawa, H. (1990). ''Seasonal changes in body shape and mass in the salamander, Hynobius nigrescens J.'' Journal of Herpetology, 24(2), 113-118.

IUCN, Conservation International, and NatureServe. 2006. Global Amphibian Assessment. < >. Accessed on 28 November 2006.

Originally submitted by: Nichole Winters (first posted 2007-01-30)
Edited by: Kellie Whittaker (2007-06-14)

Species Account Citation: AmphibiaWeb 2007 Hynobius retardatus: Hokkaido Salamander <> University of California, Berkeley, CA, USA. Accessed Jan 24, 2022.

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Citation: AmphibiaWeb. 2022. <> University of California, Berkeley, CA, USA. Accessed 24 Jan 2022.

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