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
by I can't think of a fake name April 25, 2017