Some info worth putting here for the future, taken from Tattoooedraven…
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 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.