Nishiki-Koi / 錦鯉
Koi(Carp)
Koi are believed to be fish capable of climbing upstream against rapid currents and overcoming all manner of obstacles, hence they are taken as a symbol of the strength, courage and patience to accomplish major goals.
From this comes the custom in Japan for boys to pray that they will take after koi and live their lives strongly and of hanging out carp streamers, shaped like koi, on May 5, Children's Day.
Koi
My link Children's Day