When the Roppongi Hills urban development project opened in 2003, it quickly wowed Tokyoites with its office towers, art museum, deluxe hotels, and prestigious shopping.

The most curious part of the development, however, is not its flashy design or luxury buildings, but the small garden that separates the office and cinema complex from a local TV studio.

Here, amid sunbathing office workers and locals eating lunch, sits a quiet pond ringed by reeds and irises. The pond itself dates back to the late 18th century, but that’s not all. It is filled with tiny silvery fish — fish from beyond this world.

The pond’s medaka — a species of small freshwater fish once common in flooded Japanese rice paddies, but highly susceptible to pesticides and fertilizer run-off — are descendants of those bred aboard the 1994 Columbia space shuttle.

The fish were bred as part of a series of experiments in extraterrestrial reproduction, and their descendants on earth continue to be studied by scientists.

A small sign asks people not to dump unwanted goldfish or other pets into the pond, in case they eat the precious space-fish descendants.