Japanese giant salamander

The Japanese giant salamander, known scientifically as *Andrias japonicus*, is a massive amphibian native to Japan.

It is one of only six giant salamander species in the world. This species is the third-largest salamander on Earth. It is surpassed only by the Chinese giant salamander and the South China giant salamander. In Japan, it is often called *ando*, which means giant salamander.

Because of its cultural and educational importance, the Japanese government designated it a special natural monument in 1951.

Physically, these animals are built for life in moving water. They can reach lengths of 1.5 meters and weigh up to 25 kilograms. Their skin is mottled with brown and black colors. This pattern provides camouflage against the bottoms of streams and rivers. The skin is covered in small warts, which are more concentrated on the head. Unlike many other amphibians, they lack eyelids and have very poor eyesight. To compensate, they use a lateral line system. This is a collection of sensory cells running from head to toe. These hair-like cells detect tiny vibrations in the water, much like the hair cells in a human ear. This helps them hunt in the dark.

Because they lack gills, their breathing process is very specialized. They rely on epidermal gas exchange, which means they breathe through their skin. To make this more efficient, they have large skin folds on their neck and body. These folds increase the total surface area of the skin. This allows more oxygen to enter the body and more carbon dioxide to leave. Capillaries, or tiny blood vessels, within the skin facilitate this exchange with the water. This requirement for high oxygen levels means they are restricted to clear, cool, fast-flowing mountain streams.

The distribution of the species is mostly in southwestern Japan. They are found in the western part of Honshu, parts of Shikoku, and northern Kyushu. Robust populations live in prefectures like Tottori, Hyogo, and Mie. They inhabit various freshwater environments, from small headwater streams to larger rivers 50 meters wide. Smaller adults often stay in small headwater streams. This behavior likely helps them avoid intraspecific competition, which is when members of the same species compete for resources.

The lifecycle of the Japanese giant salamander is entirely aquatic. Unlike many other salamanders, they do not move to land after metamorphosis. Instead, they remain in the water and only breach the surface to breathe air. During the breeding season in late August or early September, males migrate to find nesting sites. The most competitive males become "den masters." A den master cleans his den and guards it against other males. When a female lays her eggs, the den master stays to provide parental care. He fans the eggs with his tail to increase oxygen flow. He also performs hygienic filial cannibalism. This means he eats eggs or larvae that are dead or infected with water mold. This protects the healthy offspring from disease.

History shows how humans first encountered these giants. In the 1820s, a physician named Philipp Franz von Siebold captured an individual on Dejima Island. He shipped the specimen back to Leiden in the Netherlands. This provided Europeans with their first catalog of the species. These animals are incredibly long-lived. In the wild, they can live for nearly 80 years. One individual in a Dutch zoo lived for 52 years. They also have a very slow metabolism, allowing them to go weeks without eating.

Today, the species faces several serious conservation threats. Habitat degradation is a major issue. The construction of concrete stream banks and agricultural dams blocks migration and destroys nesting sites. Climate change also poses a risk, as more intense rainstorms may destroy stream banks. Another major challenge is introgressive hybridization. This occurs when the native Japanese giant salamander mates with the introduced Chinese giant salamander. In the Kamo River, researchers found that 95% of the population were hybrids. While the government protects them, nonprofit groups like the Japanese Giant Salamander Society work to monitor and educate the public about their declining numbers.