Takekatsu Fukuda, vice manager of the Junkudo bookstore in Fukuoka’s Chuo Ward, gazes Jan. 13 into the water tank where an Onga-suji-shima-dojo was born. (Nami Sugiura)

FUKUOKA--A rare book is one thing. But at this bookstore, an endangered loach was born in a water tank housing four of the fish, delighting researchers and spurring hope for their conservation.

A staff member at Junkudo's Fukuoka branch, which has kept the fish for display since January 2016, noticed the new occupant at the end of last year.

The discovery was met with surprise by researchers, as Onga-suji-shima-dojo--scientific name "Cobitis striata fuchigami Nakajima"--rarely breed in an artificial environment without help.

Photos of the fish were sent to Jun Nakajima, a researcher at the Fukuoka Institute of Health and Environmental Sciences who is known as "Doctor Loach."

The 42-year-old academic confirmed that the fish is loach fry, based on spots adorning the side of its body.

Onga-suji-shima-dojo, a species near to extinction, dwell in areas of the Ongagawa river in the prefecture. They measure 8 centimeters when fully grown.

During breeding season, spots on the side of the body of male fish connect to form a line.

Nakajima, who delivered a lecture at the bookstore upon the publication of a book, named a new subspecies in 2012.

Staff members at the store who handle books on science and engineering are caring for the fish with the help of nonprofit group Kitakyushu Gyobu, which collects and studies aquatic life.

Today, there are four adult loaches in the tank--and their new companion, the fry.

The young loach measured about 1 cm long by mid-January and often lurks around the bottom of the tank.

Saki Takao, a 4-year-old from Kasuga in the prefecture, squatted in front of the tank to check out the fish, saying: "Here it is. It's so cute!"

Suji-shima-dojo are typically kept in aquariums and other facilities.

Daisuke Inoue, chairman of Kitakyushu Gyobu, was stunned to learn of the birth, saying, "Something (at the bookstore) must have met some requirement for the fish to be born."

Takekatsu Fukuda, vice manager of the store, hesitated to take credit, however, saying: "We didn't do anything special. We don't have any breeding know-how."

There are 11 types of suji-shima-dojo across Japan, mainly in western areas. As all of them are indigenous species, there are concerns they may eventually die out.

For the young loach to mature and eventually breed, careful attention must be paid to changes in the water temperature and level when breeding season approaches.

Aquariums and other facilities typically apply artificial fertilization techniques.

Nakajima said he never expected a loach to be born in a bookstore.

"If the loach can naturally breed in a water tank, many aquariums will likely try to do the same, which should help with conversation of the rare suji-shima-dojo group," he said.