Koi fish are associated with good luck or fortune and a person's aspirations to improve themselves. According to New Health Guide, this meaning is derived from a collection of Chinese and Japanese legends that says the koi fish can climb the falls of the Yellow River to become a dragon.
The koi fish is often used as a tattoo by people who want to showcase their personal strength and their triumph over adversity, symbolizing that they have "climbed up the falls" and become the dragon they are today. According to the New Health Guide, the colors of the koi fish denotes an additional meaning. For instance, the red koi often represents love, while the blue koi is considered to mean reproduction.