Species account

Description
Onychodactylus fischeri is a slender, elongate salamander. 14 to 15 costal grooves. Tail is slightly longer than snout-vent length. Small elongated head with prominent eyes and moderately developed paratoids. The skin is smooth. Males and females show a number of morphometric differences.

Males have a relatively longer tail and longer forelegs. Unique among salamanders is a distinct sexual character, consisting of a hypertrophied lateral fold on the posterior surface of the male hindlegs, extending from the fifth toe to the tibia. This feature, which effectively extends the surface of the hindlegs, is most prominent during the reproductive period. Tail of the male ends in a paddle-shaped fin; tail-tip of the female is more pointed. Cloacal slit longer in males than in females (Kuzmin, 1995).  

Colour brown or grey-brown, with dark dots. A dorsal band extends over the body and tail, sometimes divided into large dark spots. Spots may be grouped at the sides, forming two indistinct dorsal stripes. 

Total length of adult animals 13 to 18 cm (Kuzmin, 1995).

Diagnosis
Onychodactylus fischeri is closely related to and very similar to O. japonicus, but differs from that species in dorsal colour pattern. Dorsal band in O. fischeri is less bright (Dunn, 1923). External sexual differences appear to be manifested to a higher degree in O. japonicus than in O. fischeri (Kuzmin, 1995); the black asperities on the inner surface of the hindlegs of both sexes in O. japonicus are not found in O. fischeri (Kuzmin, 1995) and the number of costal grooves in O. japonicus (13-14) appears to be lower on average than in O. fischeri (14-15) (Dunn, 1923).

Eggs and larvae
Two small, paired egg sacs, elliptical in shape and joined together at the distal end are attached to a stone by a mucous stalk. Many different sacs may be found attached to a single stone. Total length of each sac, including the stalk, is 45 mm. Between one and eight eggs in each sac, egg diameter 5 to 6 mm (Serbinova & Solkin, 1995). Griffin & Solkin (1995) reported five to ten eggs in each sac, with a diameter of 6 to 8 mm. Park (2005) reported two to 13 eggs per egg sac and a total clutch size varying from ten to 22, with egg diameter ranging from 5 to 7 mm.The pattern of larval development is similar to that of O. japonicus and typical for rheophilous salamanders (Regel & Epstein 1977, in Kuzmin, 1995). Spawning and hatching of larvae occur in underground spawning sites. Early larval development is subterranean and the smallest known larvae from the Russian Far East measure 34 to 39 mm. Larvae complete metamorphosis and go on land after the third or fourth hibernation at a total length of 7 to 11 cm; probably the age of sexual maturation is 8 to 9 years and maximum age 16-18 years (Griffin & Solkin, 1995; Smirina et al., 1994, in Kuzmin, 1999).

Distribution

Habitat
Onychodactylus fischeri inhabits moist, cool and shady places in mountainous regions. It occurs from 200 to 1,915 m altitude in Korea. It is associated with the upper current of small mountain streams, overgrown by mixed forests of broad-leaved trees and cedars. Streambeds should have a thick layer of pebbles and moss-covered rocks, with abundant hiding places, a high humidity and temperatures ranging from 6 to 11°C. The animals remain close to springs, permanent stream pools and waterfalls and are found under rocks, stones, fallen trees and logs (Kuzmin, 1995). Stream fidelity has been observed in mature salamanders (Griffin & Solkin, 1995).

Behaviour
The salamander may be locally abundant, but as a rule density appears to be low. The species appears to be more common at southern latitudes in Korea than in the Russian Far East. It feeds on a variable diet of aquatic, but mainly terrestrial insects, millipedes, etc. (Kuzmin, 1995).
Hibernation takes place from approximately October to late April. The animals appear when temperatures rise to 3 - 5˚C.
Breeding takes place in streams, probably mostly underground. Animals in breeding condition have been found from April to mid-July and from August to September. The peak of breeding activity is from mid-May to mid- or end of June, when water temperatures rise from 6 to 10°C (Serbinova & Solkin, 1995; Griffin & Solkin, 1995; Park, 2005).

Egg deposition and fertilization were observed in the laboratory by Serbinova & Solkin (1995): Male salamanders seem to seek out females well before spawning and remain in attendance some 10 to 20 days. The female postures on a stone with the hind part of the body in the water. Male courtship consists of moving about the female and periodically touching the vent of the female, rubbing his body on hers and staying beside her. When the female slightly arches her tail, the male suddenly extends and bends his hindlegs, and keeps them fixed in that position, unable to use them for locomotion. The female starts spawning by attaching a mucous string with the egg sacs to the stone. The male remains close to the female. When the egg sacs appear, the male starts undulating his body. He nudges the egg sacs and with his snout makes excited movements from side to side, thus dislodging the egg sacs from the female. He grasps the egg sacs with his forelegs, positioning them between his hindlegs. While pulling the egg sacs against his vent, he fertilizes the eggs. Under natural circumstances, the events pass less quietly. A large assemblage of mating salamanders was observed in a stream running through a cave in Korea (Park, 2005). For oviposition a female would move to a part of the stream where several males were present and egg sacs were already attached nearby. While attaching the egg sacs to a stone wall some 40 cm under the water surface, many males would gather and attempt to grasp the egg sacs before oviposition was completed. Males would form a mating ball, scrambling for access to the egg sacs. A total number of 173 pairs of egg sacs were found at this one underground site (Park, 2005).

Threats and conservation
This species is a habitat specialist, dependent on undisturbed old growth forest habitat with stabile streams and undisturbed stream substrate. Main threat consists of logging in stream headwaters. Onychodactylus fischeri is listed in the Red Data Books of both the USSR and Russia (IUCN, Conservation International, and NatureServe, 2005).

Observations in captivity
Of the experiments in breeding O. fischeri with the help of hormone injections, few have been successful (Serbinova & Solkin, 1995). In general, attempts to breed the species in captivity have not been very successful (references in Kuzmin, 1995).

Comments

Onychodactylus fischeri
© 1998 Max Sparreboom

Range of Onychodactylus fischeri (Kim, 2009; Fei et al., 2006), adapted from IUCN (2005) by W. Beukema & M. Sparreboom.