Hynobius dunni

Hynobius dunni. Photo by Giuseppe Molinari
Difficulty of larvae:
3/5
Difficulty of juveniles:
2/5
Difficulty of adults:
1/5
Availability:
2/5
Price:
2/5

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Salamanders & Newts of the World

Description:

Salamander with a stocky build and medium-small size (adults between 12 and 13 cm with exceptional records of 16cm in length). It has an olive/brown dorsal coloration with turquoise shades and dark spots, particularly in the juveniles, which tend to disappear with age, while the belly is gray and blue. The tail has a stocky appearance, but becomes flattened and laterally compressed during the mating period, when the specimens move in the water; in younger individuals and in some adults, it can occasionally appear bright yellow. The head is stocky and sub-oval with protruding eyes, and smooth skin. The sexual dimorphism is not particularly evident during the terrestrial phase, if not in regards of the shape of the head which, if observed from above, appears bigger and squared in the males. In the breeding period, the sexes are instead easily distinguishable, due to the appearance in the males of a brightly colored yellow throat, absent instead in the female individuals (a phenomenon also documented in other Hynobidae, such as for example Salamandrella keysterlingii, (Hasumi, M., 2001)), of a slight thickening of the forelimbs and of a more laterally compressed tail, as previously mentioned.
Male of Hynobius dunni. Photo by Giuseppe Molinari
Male of Hynobius dunni. Photo by Giuseppe Molinari
Female of Hynobius dunni. Phot by Giuseppe Molinari
Female of Hynobius dunni. Phot by Giuseppe Molinari

Distribution and Habitat:

The species is endemic to the area between Kyushu, Kumamoto, Miyazaki and Shikoku (Japan). It inhabits humid secondary forests at medium-low altitudes, where the reproduction takes place inside temporary pools, ponds, bends of watercourses and rice paddies close to woods; in environments therefore characterized by low or absent hydrodynamism and scarcity of aquatic vegetation.

Keeping:

Hynobius dunni, leading a terrestrial life for about three-quarters or half the year, can be housed in a terrarium or aquaterrarium from approximately early or mid-summer to mid-winter, at the end of which period it will be necessary, if dealing with adults and sexually mature individuals, gradually introduce them to an aquatic setup, maintaining in any case some emerged areas in order to facilitate their ascent to breathe and provide supports when they are ready to leave the aquatic environment. As far as the terrestrial phase is concerned, they appear as relatively stationary animals, and therefore do not need particularly large spaces, due to them being mainly burrowers and linked to their own refuge. A well-ventilated 60×30 base terrarium can easily be sufficient for a group of 4- 5 specimens. It is particularly important to maintain a good level of humidity both at ground level and at air level and to provide many shelters, represented by bark, moss, trunks and stones. For the substratum, a lower level of expanded clay can be used as draining material, with the top layer made out of moist coconut fibre, peat or topsoil free from harmful substances. Sphagnum and rotten wood can be a valid addition to the substrate, although not mandatory. To maintain adequate hygienic conditions inside the terrarium, the insertion of scavenger arthropods (“Cleaning Crew”) such as springtails and isopods (for example Trichorhina tomentosa) is also recommended. The substrate must be at least 10-15cm deep, to allow the animals to dig suitable shelters and keep themselves cool and humid, especially in the hottest periods. For the aquatic phase, a low pH is recommended (we recommend the use of osmosis water at least in part) and a water column equal to or greater than 10 cm, in which to insert branches at different levels (for example linden or cherry, suitably prepared and boiled before insertion), dry deciduous and catappa leaves, aquatic mosses and rocks to best simulate the stagnant environments in which they normally reproduce. The bottom of the aquatic area can be bare or with fine sand, gravel is to be strictly avoided. An aquarium filter may not be needed if large volumes of waters are used or regular water changes are performed; in any case, if you opt for the insertion of a filter, this must generate little or no current. Lighting of the terrarium is not necessary but recommended for the correct development of the plants, if present, and to maintain a correct circadian cycle for the animals. Optimum temperatures should never exceed 25°C, although the species proved to be quite hardy when briefly exposed to 27°C (hence the importance of a deep substrate). In winter, to encourage reproduction and allow for correct maturation of the gonads, it is necessary to drop temperatures below 15°C. Hibernation with maximum temperatures between 10 – 8 C° and minimums close to 0 C° have proved to be very effective.

Diet:

This species, if kept in suitable conditions, proves to be extremely voracious, arriving to accept any prey of suitable size that is offered to it. The association between keeper and food also occurs rather easily, which is why feeding with the aid of tweezers is very easy. The diet is based on annelids and arthropods, therefore earthworms, frozen Chironomus, crickets, cockroaches and isopods can be offered in captivity. As always, the greater the variety of foods offered, the better the health of our animals will be. For adult/sub-adult animals, the preys must be administered 2 to 3 times a week, with a lesser frequency in the winter and a greater frequency in the reproductive and summer periods, while the juveniles must be fed more consistently.

Breeding:

Mating can take place between early/mid December and late spring. The males, once entered the water, begin to compete for the sites (branches and other holds that will be supplied in abundant quantities) which they deem most suitable for the deposition of egg sacs by the females, from which they will be reached at a later time . Each female lays a single bifid sac measuring between 10 and 30 cm containing a variable number of eggs based on the age and state of health of the female (even more than 80 eggs per sac); these bags are normally fixed to submerged branches, more rarely to rocks and plant material. The males jealously protect the best branches, so to be the first to fertilize the sacs, fertilization which in this species is therefore external.

Egg sac of Hynobius dunni. Photo by Emanuele Biggi

Egg Hatching:

This perhaps represents the most complex passage as regards the reproduction of this species and probably that of all the Hynobiidae in general; the eggs, in fact, being in close contact with each other inside the bag, need to be regularly monitored and checked up, in order to avoid the onset of molds that could compromise the entire “brood”. First of all, it is advisable to remove the eggs from the tank or place of deposition, to avoid phenomena of cannibalism by the parents and other individuals present in the water. The sacs will be taken if possible without cutting the peduncle, completely or partially removing even the branch to which they are attached, and positioned as similar as possible to how they were oriented by the females inside containers between 5L and 20L. To combat the onset of mould, the use of very acidic water is recommended (you can proceed with an equal percentage of water from the deposition tank and new osmosis water, acidifying it by inserting catappa, oak, alder cones or coconut fiber). The insertion of an air stone or air filter for aquariums is recommended, in order to maintain minimal movement on the surface and prevent the water from stagnating. The sacs will be monitored periodically and, should mold develop on the eggs or certain embryos should stop developing, it will be advisable to make small incisions on them with the aid of a scalpel, and to remove with a syringe the compromise egg which could compromise the healthy embryos.

Developing embryos of Hynobius dunni. Photo by Emanuele Biggi
Developing embryos of Hynobius dunni. Photo by Emanuele Biggi

Growth and development of the Larvae:

Some of the larvae might need to help in getting out of the sacs, and once out, the larvae will feed on aquatic microorganisms, such as small crustaceans like Daphnia, Cyclops and nauplii of Artemia salina (well rinsed before being administered ) and other small freshwater invertebrates. Once these have reached 2-3 cm in length, they can also be fed with frozen food, such as Chironomus, and annelids of the right size, such as Enchytraeus and Lombriculus. It will gradually be necessary to separate the different larvae in different containers in relation to their size (the growth will not present the same rhythms for all), in order to avoid unpleasant episodes of cannibalism. When the larvae are close to metamorphosis (they will have all 4 limbs and will begin to reabsorb their gills) it will be advisable to lower the water level and place stones, trunks and outcropping/floating bark to facilitate their exit from the water.
The newly metamorphosed can be kept in a terrestrial environment, similar to that described for the adults, on a humid substrate (we recommend paper towels for the first few weeks in order to maintain a cleaner environment and to be able to verify that the animals defecate regularly) until reaching sexual maturity, which will occur on average between the third and fourth year of life. The juveniles will be fed with Chironomus and Enchytraeus, administered with tweezers, and/or with l1/l2 stages of crickets and cockroaches or with small isopods, coleoptera or diptera.

Larva of Hynobius dunni. Photo by Giuseppe Molinari
Larva of Hynobius dunni. Photo by Giuseppe Molinari

Ethological notes:

It is a species that has both diurnal and nocturnal habits, especially at dusk. During the mating period, the individuals are clearly visible and can often be seen both in the water and outside the shelters, while in the terrestrial phase, during the rest of the year, they will tend to remain in their dens, unless food is offered to them, and will therefore be less visible. As already mentioned, it is an extremely voracious species that will easily engage in a feeding frenzy and it is therefore recommended to pay maximum attention during feeding, trying to distance the individuals as much as possible from each other, to avoid bites between conspecifics which could cause lesions that can be attacked secondarily by fungi and other pathogens. Outside of the feeding phase, they do not show particular territorial behaviors and tolerate the presence of conspecifics well.

Availability:

It is not a common specie in the hobby, as there are not many keepers then breed them.

Legislation:

They are not protected and no permit is required to keep them.

About the Authors...

Jacopo Martino
Jacopo Martino

Jacopo Martino, 22 years old, is a student attending the third year of the Faculty of Biological Sciences of the “La Sapienza” University of Rome. He is also an assistant at the laboratory of the Department of Zoology of the homonymous structure.

Special collaborator of the Arthropoda Live Museum cultural association.

For the past 9 years he has been breeding arthropods and amphibians, in particular, insects and urodela, but also crustaceans, arachnids, anura and two species of Gymnophiona.

“I would like to be able to work one day with salamanders of the genus Bolitoglossa or with other species of caecilian, as these animals are very little studied and still mysterious.”

Giuseppe Molinari
Giuseppe Molinari

Giuseppe Molinari, born in 1996 in Cesena, spent his childhood in the Tuscan-Romagna Apennines where he became passionate about naturalistic subjects.

He is currently graduating in Natural Sciences at the University of Bologna.

He is passionate about wildlife photography with a predilection for herpetofauna and he collaborates as a volunteer in various LIFE projects within the National Park of the Casentinesi Forests.

It has been breeding caudata continuously since 2014, in particular he focuses on species of Asian origin.

References

Citations: Hasumi, M. (2001). Secondary sexual characteristic of the salamander Salamandrella keyserlingii: Throat coloration. Herpetological Review, 32(4), 223.