According to Chinese tradition, if the Koi swims up to the top of the waterfall, it becomes a dragon.
Japanese adapted the idea.
So Koi indicates ascendant, prosperity and more.
In Edo Period (1603-1868) Samurai family used to decorate Koinobori in their yard for wishing for their children’s succeed in life around May 5th.
Koinobori meaning “carp streamer” in Japanese, are carp-shaped wind socks traditionally flown in Japan to celebrate Tango no sekku, a traditional calendrical event which is now designated a national holiday; Children’s Day on May 5th.
I have seen Koinobori, which are carp-shaped wind socks in California.
What an imagination, flying fishes in the sky, isn’t it?