Amphibians
Japanese Giant Salamander
Andrias japonicus · also called ōsanshōuo, giant pepper fish
The Japanese giant salamander is a living fossil the size of a small dog, hidden in the clear cold rivers of western Japan. It has changed little in tens of millions of years, it breathes through its wrinkled skin, and it can live long enough to see out a human generation.
Overview
Japanese giant salamanders inhabit cool, fast-flowing, well-oxygenated mountain rivers and streams with rocky or gravel beds and plenty of undercut banks and boulders to hide beneath. They are found in western Honshu, Shikoku, and Kyushu. They are almost entirely aquatic and nocturnal, spending the day wedged in a crevice or burrow and emerging at night to forage slowly along the streambed. They are highly sedentary — an individual may use the same stretch of river for decades.
An ancient, skin-breathing giant
The species belongs to the family Cryptobranchidae, the “giant salamanders,” alongside the Chinese giant salamander and the North American hellbender. Its body is a design for life pinned to a cold streambed:
- Skin breathing. With gills lost and lungs reduced, it absorbs oxygen across its skin, and the loose, wavy folds along the flanks exist purely to add surface area.
- Reduced eyes. Vision is minimal; it senses prey and threats through skin sensory organs that detect water movement, plus smell.
- A flattened head and body to slip under rocks and resist the current.
- Peppery mucus. When handled or attacked it exudes a sticky white secretion with a sharp smell, giving it the folk name “giant pepper fish.”
Feeding and breeding
The salamander is an ambush predator, taking fish, crayfish, insects, worms, frogs, and even small mammals with a rapid sideways strike. Breeding happens in late summer: a large “den master” male occupies a nesting burrow in a riverbank and admits multiple females to lay their eggs there, after which he guards and aerates the clutch — sometimes hundreds of eggs from several females — driving off intruders, including other salamanders that would eat the eggs.
Threats and conservation
The Japanese giant salamander is Vulnerable and declining. River engineering — dams, weirs, and concrete channelisation — fragments its habitat and buries the gravel and bank burrows it depends on, and siltation and pollution from farming and forestry degrade its water. A newer and serious threat is hybridisation: Chinese giant salamanders brought to Japan for food have entered the wild and are interbreeding with the native species, genetically swamping some populations. The salamander is legally protected in Japan as a “Special Natural Monument,” and conservation work includes building fish-and-salamander passes around barriers, restoring stream habitat, and removing hybrids.
Japanese Giant Salamander: common questions
How big is the Japanese giant salamander?
It reaches about 1.5 metres and 25 kilograms, making it the second-largest amphibian in the world after its close relative the Chinese giant salamander (which can be slightly larger). The North American hellbender, in the same family, is a distant third at up to about 0.7 metres. These "giant salamanders" are an ancient lineage — nearly identical fossils are around 30 million years old, and the family split from other salamanders far earlier.
How does a giant salamander breathe if it has no gills or working lungs?
Through its skin. An adult Japanese giant salamander gets nearly all of its oxygen by diffusion across its skin, and the deeply wrinkled, baggy folds running along its body and legs exist to maximise the surface area available. It has simple lungs but uses them mainly for buoyancy. This is why it can only live in water that is cold and fast enough to stay highly oxygenated — warm, still, or polluted water suffocates it.
How does a nearly blind salamander catch fish?
It waits. The Japanese giant salamander is a nocturnal ambush predator that lies still on the streambed, often at the mouth of an undercut bank or a burrow, and detects prey by the pressure waves and vibrations it makes in the water, picked up by sensory nodes in the skin, plus a good sense of smell. When a fish or crayfish comes within range, the salamander turns its whole head and body sideways and snaps, engulfing the prey with a sudden suction gape.
Why is the Japanese giant salamander threatened?
Its rivers have been extensively dammed and channelised, which blocks the salamanders' movements to breeding sites and removes the gravel-bottomed, bank-burrow habitat they need, and agriculture and forestry have added silt and pollution. On top of this, Chinese giant salamanders imported for the food trade have escaped or been released into Japanese rivers and are interbreeding with the native species, producing hybrids that are diluting the wild gene pool — now considered one of the most serious threats. The salamander is a protected "Special Natural Monument" in Japan.