Japanese giant salamanders have wrinkled skin mottled with varying patterns of black and shades of brown. Some appear quite dark, while others have lighter patches. They have an elongated body, a long, broad tail and two pairs of legs that are roughly similar in size. Their eyes are tiny and positioned on top of their broad, flat head.
When aggravated or stressed, Japanese giant salamanders secrete a sticky, white mucus that is toxic to predators. The sticky secretion smells like Japanese peppers and gives them the name "big pepper fish."
Like other amphibians, the Japanese giant salamander has smooth skin rather than scales. The skin acts as a respiratory surface where oxygen enters the body and carbon dioxide is released. Flaps of skin that run laterally increase the surface area for respiration. Rocking gently in the water helps oxygenate its body.
Giant salamanders have a single lung, which is not used for breathing but for buoyancy control, like a fish's swim bladder. Although they are almost always submerged in water, giant salamanders can survive periods of time above the surface as long as their skin remains moist.
There are three species of regionally distinct giant salamanders within the family: Japanese, Chinese, and the North American hellbender. The Japanese giant salamander is the second largest salamander in the world. The largest is the Chinese giant salamander, which grows to 6 feet (1.8 meters). These wrinkled denizens of cold water belong to the same family as North America's hellbender. The Chinese giant salamander has fewer tubercles (bumps) on its head than the Japanese giant salamander.
The Japanese giant salamander lives in streams on a few Japanese islands. The main concentration is on western Honshu Island, though there is spotty distribution on northern Kyushu Island and Shikoku Island. Giant salamanders live in cold, fast flowing water with plenty of oxygen. These streams usually have rocky or gravel bottoms with riffles. The animals hide under large rocks along the water's edge. During the upstream migration to their breeding sites, they will emerge from the water in order to navigate around natural or manmade dams.
Japanese giant salamanders have poor vision and have to rely on other senses, including smell and touch, to detect prey. They feed on a variety of prey, including fish, smaller salamanders, worms, insects, crayfish and snails—catching them with a rapid sideways snap of the mouth. Japanese giant salamanders also feed on turtles, snakes, and small mammals. They have teeth on both the upper and lower jaws, plus a w-shaped second row of teeth on the upper jaw. This dentition allows the giant salamander to trap prey in its mouth and bite through bone. It has an extremely slow metabolism and can go for weeks without eating if necessary.
Unfortunately, they will ingest litter, especially food wrappers containing residual odors.
At the Smithsonian's National Zoo, the Japanese giant salamanders eat fish and shrimp.
Males reach sexual maturity at 12 inches (30 centimeters), females at 16 inches (40 centimeters).
Unusual for salamanders, this species uses external fertilization and lays eggs in strings rather than clumps. Nests have a single entrance opening underwater. Favorable nest sites may be used during successive years. Females enter the nests more than once beginning in August to September and lay their eggs in the cavity where the males fertilize them. Females lay between 400 and 600 eggs in the nest, held together by a gelatinous material like a string of pearls.
Large, heavy males (den-masters) attempt to monopolize the nest sites. As long as pregnant females are in the nest, the den-master allows other males to enter. After spawning is complete, however, the den-master guards his burrow and will eat intruders like crabs and newts that would otherwise feed on the larvae. He also chases and attacks other male giant salamanders that intrude and try to fertilize the eggs. Dominance rank of den-masters among males attempting to breed appears to be strong, as evidenced by injuries sustained by males during the breeding season. Most wounds heal quickly. The den-master periodically turns the eggs over to aerate them by wrapping his body around the string of eggs and flipping his body over.
Hatching occurs by late October. When larvae hatch, they are 0.10 inches (30 millimeters) and start feeding after they absorb their yolk. Some cannibalism occurs among siblings. The larvae stay in the nest until January.
One-year-old larvae measure about 0.25 inches (100 millimeters), 3-year-olds about 0.5 inches (200 millimeter). At this size, larvae start losing their gills. Metamorphosis is complete after about three years. Very few larvae survive to maturity.
These salamanders are nocturnal.
The species is presumed to take at least five years to reach maturity and is extremely long-lived. A Japanese giant salamander at the Amsterdam Zoo lived for 52 years.
Japanese giant salamanders are classified as near threatened on the IUCN Red List, and their population may be declining. They are threatened by habitat degradation. When rivers are channeled with cement to control flooding, it reduces the range and number of prey animals they can catch. Dams and culverts prevent them migrating upstream, while deforestation increases soil erosion which silts up the rivers.
About 3,000 Japanese giant salamanders live in the wild, including about 800 that are tagged. It is listed in Appendix I of the Convention of International Trade of Endangered Species Conservation, which protects it from international trade.
The Zoo hopes to become the first zoo in the United States to successfully breed Japanese giant salamanders by mimicking the water temperature, photo periods, and living conditions of the salamanders at the Asa Zoo in Japan.