By YURI KAGEYAMA, TOKYO, go.com

Thousands of Japanese marched to celebrate the switching off of the last of their nation’s 50 nuclear reactors Saturday, waving banners shaped as giant fish that have become a potent anti-nuclear symbol.

Japan was without electricity from nuclear power for the first time in four decades when the reactor at Tomari nuclear plant on the northern island of Hokkaido went offline for mandatory routine maintenance.

After last year’s March 11 quake and tsunami set off meltdowns at the Fukushima Dai-ichi plant, no reactor halted for checkups has been restarted amid public worries about the safety of nuclear technology.Today is a historic day,” Masashi Ishikawa shouted to a crowd gathered at a Tokyo park, some holding traditional “koinobori” carp-shaped banners for Children’s Day that have become a symbol of the anti-nuclear movement.

“There are so many nuclear plants, but not a single one will be up and running today, and that’s because of our efforts,” Ishikawa said.

The activists said it is fitting that the day Japan stopped nuclear power coincides with Children’s Day because of their concerns about protecting children from radiation, which Fukushima Dai-ichi is still spewing into the air and water.

The government has been eager to restart nuclear reactors, warning about blackouts and rising carbon emissions as Japan is forced to turn to oil and gas for energy.

Japan now requires reactors to pass new tests to withstand quakes and tsunami and to gain local residents’ approval before restarting.

Response from people living near nuclear plants has been mixed, with some wanting them back in operation because of jobs, subsidies and other benefits to the local economy.

The mayor of Tomari city, Hiroomi Makino, is among those who support nuclear power. “There may be various ways of thinking but it’s extremely regrettable,” he said of the shutdown.

Major protests, like the one Saturday, have been generally limited to urban areas like Tokyo, which had received electricity from faraway nuclear plants, including Fukushima Dai-ichi.

Before the nuclear crisis, Japan relied on nuclear power for a third of its electricity.

The crowd at the anti-nuclear rally, estimated at 5,500 by organizers, shrugged off government warnings about a power shortage. If anything, they said, with the reactors going offline one by one, it was clear the nation didn’t really need nuclear power.

Whether Japan will suffer a sharp power crunch is still unclear.

Electricity shortages are expected only at peak periods, such as the middle of the day in hot weather, and critics of nuclear power say proponents are exaggerating the consequences to win public approval to restart reactors.

Hokkaido Electric Power Co. spokesman Hisatoshi Kibayashi said the shutdown was completed late Saturday.

The Hokkaido Tomari plant has three reactors, but the other two had been halted earlier. Before March 11 last year, the nation had 54 nuclear reactors, but four of the six reactors at Fukushima Dai-ichi are being decommissioned because of the disaster.Yoko Kataoka, a retired baker who was dancing to the music at the rally waving a small paper carp, said she was happy the reactor was being turned off.

“Let’s leave an Earth where our children and grandchildren can all play without worries,” she said, wearing a shirt that had, “No thank you, nukes,” handwritten on the back.