Japanese killifish swim in a rooftop pond in Tokyo's Roppongi Hills

Killifish 鱂魚

• 日本語
  

Killifish survive swimmingly on rooftop

BY TORU IGARASHI, THE ASAHI SHIMBUN2008/12/10

Japanese killifish swim in a rooftop pond in Tokyo's Roppongi Hills. (THE ASAHI SHIMBUN)The Keyakizaka Complex roof garden is surrounded by Roppongi Hills high-rises.(TERUO KASHIYAMA/ THE ASAHI SHIMBUN)

On a rooftop 45 meters above ground, amid posh Roppongi Hills high-rises in central Tokyo, schools of killifish leisurely swim in a pond surrounded by trees and rice paddies.

Nine medaka, or Japanese killifish designated by the government as a threatened species, were released there five years ago.

Thanks to an absence of natural enemies, they have multiplied to several hundred.

The fish make their home on the roof of the Keyakizaka Complex, a seven-story building housing a cinema complex and shopping malls.

The roof garden is designed as a recreation of an old farming area. The 40-square-meter pond is 20 centimeters deep and filled with unheated, mechanically circulated rain water.

In the summer of 2003, two months after the Roppongi Hills complex opened, the Hills operator released seven grayish kuro-medaka and two whitish shiro-medaka in the pond. Sixteen Tokyo daruma pond frogs along with 44 loaches and others completed the aquatic family.

They have all increased in number.

Shuji Tachikawa, a former associate professor of insect ecology at the Tokyo University of Agriculture, studied how the creatures were getting along soon after their release.

"The killifish have propagated probably because there are no predators such as egrets and herons," said Tachikawa, 67, an official of the nonprofit Association for Nature Restoration and Conservation, Japan.

"The water is clean and its temperature has been kept at appropriate levels, so the environment was just good for killifish," he said.

With the soil and water weighing 3,650 tons, the roof garden is, in fact, designed to serve as part of an earthquake shock-suppression system.

The garden is open for events and student school trips by reservation only.

Kuro-medaka killifish varieties used to be seen almost everywhere water was found--in rice paddies, streams and ponds.

Their numbers nose-dived as rice fields disappeared and irrigation canals were covered over with concrete. The fish were designated as vulnerable in the then Environment Agency's red list in 1999.

Killifish kept as pets these days are often the reddish hi-medaka variety.

A sixth-grader from Shizuoka Prefecture, who visited Roppongi Hills on a school trip, was surprised to see killifish for the first time at "a place like this" in the metropolis.

Tamotsu Hara, 78, head of the Hills community association, used to run a goldfish shop in the area and kept killifish as well.

"I feel nostalgic," Hara said. "They bring back memories of those good old days I have forgotten."(IHT/Asahi: December 10,2008)

Japanese killifish swim in a rooftop pond in Tokyo's Roppongi Hills. (THE ASAHI SHIMBUN)