Missed Something Here

PLEASE WAIT LOADING ,,,,,,,,,
Those in the know, whoever you are, could you explain when koi became, in the words of Yuri Kageyama of AP:
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.

(Link)
Except for the coincidental occurrence of the shutdown of the Tomari #3 reactor on the Tango no Sekku holiday, is there some other reason heretofore not widely stated for carp streamers or the giant images of any other fish being "potent anti-nuclear" symbols? Please let me know in comments.

Furthermore, is it not a wee bit misleading to refer to a crowd of 5,500 in Tokyo as "thousands of Japanese"? A crowd of 5,500 is less than five Odakyu express trains pulling into Shinjuku.

By the way, this week's heavy rains wiped out the display of Japan's largest koi nobori (J), trimmed parades and eliminated numerous scheduled outdoor celebrations of spring (J) -- as well as a hacking out an unhealthy chunk of the seasonal revenues of major tourist sites.


Later - Here are some anti-nuclear protest/celebration crowd figures from other major cities:

Sapporo: 450
Nagoya: 250
Osaka: 600
Fukuoka: 50