Six rare and highly protected Japanese giant salamanders bred and raised at the Asa Zoological Park in the city of Hiroshima were sent last week to the Smithsonian National Zoological Park in Washington, according to officials of the two zoos.

The two 19-year-old females and four 11-year-olds — two males and two females — were all born at Asa, the only zoo in the world where the species has been successfully bred on a regular basis.

It marks the first time that Japan has sent any of the river-dwelling creatures, regarded here as a national treasure, to overseas zoos in more than a decade. A detailed contract was concluded between the two zoos in 2006 for the six salamanders.