Rana kobai
Subgenus: Rana
family: Ranidae
Species Description: Matsui M 2011 On the brown frogs from the Ryukyu Archipelago, Japan, with descripitons of two new species (Amphibia, Anura). Current Herpetology 30: 111-128.

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Conservation Status (definitions)
IUCN (Red List) Status
Other International Status None
National Status None
Regional Status None



Rana kobai is a small, relatively slender member of the Rana genus, with females being larger than males. Its snout-vent length ranges 32-41 mm in males, and 35-46 mm in females. The dorsum, sides, tarsus, and rear portion of upper eyelids are scattered with small tubercles which have white asperities. The throat, chest, and abdomen are smooth. The head is longer than it is wide, with a pointed snout. The snout tip is rounded when viewed from the side, and extends past the lower jaw. The nostrils are located close to the tip of the snout. A circular, distinct tympanum is present, about three-fifths the width of the eye. The interorbital distance is often slightly less than the width of the upper eyelids. Vomerine teeth are present in two small, oval series. The tongue is notched, and lacks papilla. No vocal sac (or vocal opening) is present. A supratympanic fold extends from the posterior of the eye to just above the insertion of the arm. Behind this is a thick dorsolateral fold extending to the groin. The forelimbs in R. kobai are stout, with slender, unwebbed digits. Fingertips are rounded, but lack grooves. Three large palmar tubercles are present, as are distinct subarticulate tubercles (supernumerary tubercles are indistinct). A distinct, cream colored nuptial pad covers the first digit, extending from the base to the subarticulate tubercle. R. kobai has long hind limbs, which are less than three times the length of the forelimbs. The feet are moderately webbed, and the tips of the toes resemble the tips of the fingers. The subarticulate tubercles are prominent, as is the inner metatarsal tubercle (Matsui 2012).

R. kobai has small tubercles with asperities present on the dorsum, sides, and tarsus, as well as on the posterior half of the eyelids. The snout is pointed, and the tympana are somewhat large, with a diameter three-fifths that of the eye. A dark band extends over the tympanum, and a white stripe is present at the top of the upper lip. The dorsolateral fold is thicker than that of its close relative, R. ulma. No vocal sac is present in males. Dark spots are present on the venter, but are not clear. Digit tips are swollen, but are not grooved. Eggs are not laid in a globular mass, as is done by some closely related species (Matsui 2012).

Coloration: In preservation, the dorsum of R. kobai is light brown. A narrow, dark grey bar is present between the eyes, and a faint gray chevron is present in in the interscapular region. The dorsolateral fold has a cream coloration. A distinct brown coloration passes over the eye and tympanum, extending to the insertion of the arm. The upper surfaces of the limbs are marked with dark crossbars. The dorsal coloration of the limbs and the area around the vent is a darker brown than the rest of the body. The posterior portion of the thigh is dusted with a brownish coloration. Brown dots are present on the white ventral surface, particularly visible around the chin. The ventral surface of the feet is light grey (Matsui 2012).

Variation: Females are larger than males, but have weaker asperities on the back. In populations on Amamioshima, the relative size of the tympanum is larger for males than females, and the toe webbing of males is better developed, but females have a larger snout length relative to their eye (the snout length is longer than the eye for females, but over fifty percent of males have a snout length shorter than or equal to the length of the eye). In the Tokunoshima population, males have a greater relative foot size than females (Matsui 2012).

Tadpole morphology: R. kobai tadpoles at stage 35 have a total length of around 28.8 mm, with a head-body length of 10.6 mm. Tadpoles at stage 36 have a total length of around 30.3 mm, with a head-body length of 10.4 mm. The tadpoles are of a normal type, and do not have ventral modification (such as the sucker like structure seen in R. sauteri). Head and body have a flattened dorsal surface, but a rounded (spheroid) ventral portion. The snout is rounded, with eyes located dorsolaterally, which are not visible from below. Open, dorsolateral nostrils are located closer to the tip of the snout than to the eye. An oral disc is present anteroventrally. The tail is long and muscular, and tapers to a rounded tip (Matsui 2012).

Juveniles at metamorphosis measure about 9.6-10.6 mm in snout-vent length (Matsui 2012).

Tadpole coloration: In preservation, the dorsal and lateral surfaces of tadpoles are light brown. The venter is grey, scattered with silver. Silver and black spots are scattered on the tail. (Matsui 2012).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: Japan

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R. kobai is only known from Amami Oshima, Kakeromajina, and Tokunoshima, islands of the Amami Island Group, Central Ryukyus, Japan (Matsui 2012).

Life History, Abundance, Activity, and Special Behaviors

Breeding occurs in winter, typically from late November to early January, but may continue until as late as April. Eggs are laid in small clumps (with a clutch size of around 510 eggs) in locations such as the headwaters of montane streams, springs near trails, ponds, and other marsh-like environments, with water temperatures ranging from 8.5 to 16 °C. Metamorphosis occurs by the end of March for most individuals, although some may not undergo metamorphosis until after May (Matsui 2012).

The calls of male R. kobai are similar to those of its close relative, R. ulma. The call consists of 5-8 notes over a 500-1000 ms duration. The fundamental frequency is around 1800 Hz (Matsui 2012).


The species authority for R. kobai is Masafumi Matsui.

R. kobai is named for the late Dr. Kazuo Koba, Professor Emeritus of Kumamoto University, who helped pioneer herpetological survey in the Amami island group (Matsui 2012).

R. kobai is most closely related to R. ulma, another species of brown frog located on nearby islands. Other close relatives include R. tsushimensis from Tsushima Island and R. sauteri from Taiwan (Matsui 2012).

R. kobai has a diploid number of 26 chromosomes, where five of the pairs are large, and 8 of the pairs are smaller (Matsui 2012).


Matsui, M (2011). ''On the brown frogs from the Ryukyu Archipelago, Japan, with descripitons of two new species (Amphibia, Anura).'' Current Herpetology, 30, 111-128.

Written by John Cavagnaro (john.cavagnaro AT, University of California Berkeley
First submitted 2012-04-30
Edited by Mingna (Vicky) Zhuang (2012-10-04)

Species Account Citation: AmphibiaWeb 2012 Rana kobai: Amami-Aka-gaeru <> University of California, Berkeley, CA, USA. Accessed Mar 28, 2017.

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Citation: AmphibiaWeb. 2017. <> University of California, Berkeley, CA, USA. Accessed 28 Mar 2017.

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