It's basically the root of all hatred between students and teachers
teacher: hey students, guess what!
students: what?
teacher: we're gonna have a test today
students: ...
it's basically an ornamental varieties of domesticated carp, or more well known as Koi(I'm talking about the fish). It is also the title of the book NISHIKIGOI The Swimming Jewel by Manabu Ogata
yeah, the word Nishikigoi is technically Japanese so it's kinda hard to use it in an English sentence