Japanese giant salamanders (Andrias japonicus), also known as オオサンショウウオ, is one of the three species of giant salamander. There are two genera belonging to the family of Cryptobranchidae, Cryptobranchus and Andrias.
Cryptobranchus alleganiensis, the only species of the former, lives in the rocky and clear streams of USA. Local people name this species as hellbender, mud devil, devil dog for its creepy appearance.
Andrias davidianus which naturally distributed in China was introduced into Japan in 1970s as a novel food. However, it was released intendedly to the wild and hybridized with native Andrias japonicus. Currently, over 90% of the individuals in Kamogawa are hybrids. The hybrid is distinct to A. japonicus from a significantly bigger body size and a swelled head.
During this trip, we found one “young” adult and one hatchling of A. japonicus. They dwell in rocky streams with a high concentration of oxygen, where males defend their territories under big rocks during the mating season (appr. July-September). It would take at least 5 years for a hatchling to reach sexual maturity, and once it finally becomes an adult, it only grows appr. 1 cm per year. The adult we found was about 60 cm in body length, which means it was only 20 or 25 years old, for a species that can reach to 1.5 m, it was still young. Hatchlings were hard to be found in the wild, we were lucky to spot one when it was swimming in a shallow bankside. This hatchling might be the very first born individual that year as we can still observe its external branchia around its neck.
Currently, hybridization with A. davidianus and habitats destruction were the two major threat to A. japonicus. The government of Japan assigned this species as a “natural momentum” and put lots of efforts on conservation. People can easily see a giant salamander as long as going to a proper habitat and looking for it.