Japanese giant salamanders have been bred indoors for the first time in Japan, a facility in Shimane Prefecture trying to conserve the huge, river-dwelling amphibians announced.

The Mizuho Hanzake Field Museum said a 24-year-old female salamander named Sachiko was found Wednesday morning to have laid around 500 eggs in an artificial nest inside an indoor display tank. It said the eggs are thought to have been fertilized because a male salamander named Daigoro is guarding the nest. The males of the species protect the nest until the eggs hatch and the larvae leave.

Japanese giant salamanders, which can grow 1.5 meters long, enjoy the highest level of governmental protection in the nation. The species was designated a natural monument in 1952.

But despite their lofty status, giant salamander habitats in Japan remain largely unprotected, except for a few reserves. Their habitats have been greatly reduced and fragmented due especially to the construction of dams and concrete riverbanks intended for flood and erosion control and irrigation purposes.