A lot of people keep koi for different reasons. Some say for the prestige, others for the money, still others for the simple joy of having them around. Either way and whether they admit this or not, they undoubtedly keep koi because for them, there is a special meaning of koi fish.
Koi fish meaning holds much significance in some cultures. In China, they are sometimes used as models when demonstrating the "yin yang" symbol, which illustrates the universal concept of polarity: good and evil, dark and light, day and night. In fact, fish itself are thought to bring luck or good fortune, because the Chinese word for "abundance" has the same sound as the Chinese word for fish. In Buddhism, koi fish meaning signifies courage, as humans are thought to "swim" without fear through the "ocean of suffering." This symbolism is reminiscent of an old legend about the koi fish, which climbs successfully up towards the falls at a point called Dragon Gate on the Yellow River, and magically turns into a dragon.
Probably because China and Japan have the koi in common, the Japanese are also familiar with this myth; however, the representation they place on the koi is more pronounced. The meaning of koi for them is the ideal of strength of purpose and perseverance in adversity. It is inherent in the koi's nature to travel upstream, despite the flow and power of the current, and these are qualities that have especially endeared these fish to the Japanese. They have further enhanced the story to mean worldly aspiration and advancement, in connection to the koi's transformation into a dragon.
The Japanese also believe that koi fish meaning refers to masculinity, for every year there is an annual Boys Day Festival which involves the creation of a kite in the shape of a koi, where each kite represents each son in the family. The more kites, the more sons, the more prosperous a family is thought to be! Koi fish meaning has then been synonymous to prosperity, good luck, and — because sons are thought to be responsible for giving the world a chance to propagate — long life.
But the most interesting koi fish meaning that the Japanese have come up with is love. The kanji character for heart or "kokoro" is included in the kanji characters of both "love" and "koi," where koi signifies romantic love for the opposite sex. Even so, koi has been designated to represent "love and friendship" in their country.
Koi were cultivated in Japan primarily for color, although it is recorded that they originated in China, where they were known then as the common carp and bred as a food source. In Japan therefore, the literal meaning of koi would be carp. If one were to speak of the colorful fish kept in garden ponds, the proper term would be nishikigoi. But whether they are called koi or nishikigoi by us, they remain our favorite pets and the world's most beautiful ornamental freshwater fish.