The Japanese giant salamander, a rare amphibian known as a "living fossil", is at risk of disappearing as a distinct species as interbreeding with its Chinese relative increases.
Over the years, hybrids between Japanese and Chinese giant salamanders have proliferated in western Japan, sounding alarm bells and touching off a flurry of activities to preserve the native species.
The Japanese giant salamander, which at up to 1.5 metres in length is the world's second-largest amphibian after its Chinese relative, inhabits rivers and streams in the Chugoku, Kinki and Chubu regions of western and central Honshu, Japan's main island, and parts of Shikoku and Kyushu islands.
The term "living fossil" is used because giant salamanders have barely changed from their ancestors of 30 million years ago.
Local authorities and biologists in Kyoto Prefecture, where the hybridisation problem is especially acute, and other prefectures are investigating how much hybridisation between Japanese and Chinese salamanders has spread.
Chinese giant salamanders were first imported to Japan for eating or ornamental purposes in the 1970s, before Tokyo acceded to the Convention on International Trade in Endangered Species of Wild Fauna and Flora, which bans their trade.
Some imports either escaped or were released into the wild and interbred with the natives. "The native species is a national treasure," a local official in Uda said. "We can't afford to allow it to go extinct. We want to stop the increase in hybrids."
Amphibian expert Masafumi Matsui, a Kyoto University biology professor, blamed humans for harming nature by not thinking through the consequences of their actions. "This has happened because the Chinese salamander was imported without much consideration," he said.
"Humans are disrupting the evolution of living creatures and the history of the creation of diversification that goes on over an immense amount of time, but they are not aware of this fact because they do not see tangible damage, as in the case of agricultural disasters."