According to Japanese legend, if a koi succeeded in climbing the falls at a point called Dragon Gate on the Yellow River, it would be transformed into a dragon. Based on that legend, it became a symbol of worldly aspiration and advancement.
More generally, the Japanese associate koi (also known as carp) with perseverance in adversity and strength of purpose. Because of its strength and determination to overcome obstacles, it stands for courage and the ability to attain high goals.
A koi tattoo is supposed to represent different things it just depends on the color and the amount of them and the direction they are swimming in the stream. 5 golden koi is supposed to represent eternal wealth and well being. Each color represents a specific meaning. Some people believe that the color of Koi Tattoo on your body should be in harmony with you and your surroundings.
Symbolic in the Buddhism to represent courage. Humans “swim” through the “ocean of suffering” without fear, just like a fish swims through water. It means good fortune or luck.