Lethargic River Resident

Saturday-Sunday, January 11-12, 2025

Lethargic River Resident

Today’s special animal friend is the Japanese giant salamander, Andrias japonicus. A member of the Cryptobranchidae family, this amphibian grows over five feet long and weighs up to 55 lbs. (according to Wikipedia) or 88 lbs., according to the Detroit Zoo. The closely related Chinese and South Chinese giant salamander are even bigger, while the North American cousin, the hellbender, is only a couple of feet long and weighs around 3 lbs. The Japanese giant salamander can interbreed with the Chinese one, which has been introduced to Japan, and why on earth would anyone do that unless they plan a Giant Amphibian Apocalypse?

When it’s not eating people whole and stomping skyscrapers to the ground or snapping up bullet trains as if they were earthworms, the Japanese giant salamander lies at the bottom of a cold, swift-moving stream, breathing through its skin because it has no gills. They have large skin folds in the neck area, increasing their skin surface to facilitate oxygen uptake. They are a grayish-brown shade with gray and brown mottling, like the bottom of a stream. They have warty nodules on their neck and head, like little crustaceans or moss on a rock. Reflect upon the possibility that one might be right in front of you as you admire some Nature in Japan ... but you don’t see it.

Males and females are nearly identical in this species. Both feed on insects, frogs, and fish, rarely lifting even their heads above water. They just lie there. They have very poor eyesight and use a lateral-line motion sensing system to detect the movement of prey. Being a low-exertion species, they can go long periods without eating and can live up to 80 years.

Adults move upstream to reproduce. Males establish breeding dens where females, having selected a mate, lay eggs. Males guard the eggs, which they fertilize with sperm-containing “milt,” to prevent other males’ sneaking in and fertilizing. The females don’t care. Tiny larvae emerge from the eggs. They develop gills and limbs; the gills are lost as they mature.

Video of a Japanese giant salamander eating a rival’s eggs (playback only available on YouTube)

Threats to the Japanese giant salamander include interbreeding with the Chinese version. They also suffer habitat loss due to pollution and silting of streams and rivers, as well as loss of flowing water because of dams. They are classed as Near Vulnerable by IUCN and are protected from trade by CITES. They are found in a number of zoos around the world, and captive breeding programs have experienced some success.

The town of Yubara, known for medicinal hot baths, holds a Giant Salamander Festival each year on August 8. Located in the southern part of Honshu, Yubara has a population around 3,000. It is a picturesque little town, situated in a wooded ravine along the Asahi River. The river is dammed at this point, which is far from ideal for the giant salamanders.