Koi fish are common tattoo for the Yakuza

1) "Probably surprising to many westerners is the large of amount of ancient myth that surrounds these beautiful fish in the Orient and their elevated status there." "(koi is Japanese for carp)" "the koi is more than just a colorful and collectible fish. It is also one of the most popular and beautiful of Japanese tattoo symbols – a beauty which belies its symbolic meaning. Although Chinese in origin, the carp is now widely celebrated in Japan, particularly for its manly qualities. It is said to climb waterfalls bravely, and, if caught, it lies upon the cutting board awaiting the knife without a quiver, not unlike a samurai (warrior) facing a sword. This theme dates back to ancient China, where a legend tells of how any koi that succeeded in climbing the falls at a point called Dragon Gate (on the Yellow River) would be transformed into a dragon. Based on that legend, it became a symbol of worldly aspiration and advancement. Eventually, the stoic fish came to be associated with so many masculine and positive qualities that it was appropriated for the annual Boys' Day Festival in Japan where even today colorful, streaming koi flags are traditionally displayed for each son in the family. In tattoo imagery, especially in combination with flowing water, it symbolizes much the same: courage, the ability to attain high goals, and overcoming life's difficulties." Source and further information: http://www.tattoosymbol.com/articles/koi.html 2) "Koi are considered a manly symbol, especially after it was appropriated by the Boys' Day Festival in Japan. According to legend, the koi climb the waterfall bravely, and if they are caught, they face their death on the cutting board bravely, like samuri. Other Japanese meanings include perseverance and strength. In China, it is believed that if the koi succeeded in climbing to "Dragon Gate" on the Yellow River, the koi will be transformed into dragons. Because of the Chinese legend, koi are considered a symbol of advancement and aspiration. When used in tattoos, especially with running water, the koi is meant to symbolize courage and the ability to attain goals and to overcome life's difficulties. When the koi in the tattoo is shown swimming upstream, it can be used to mean that the tattooee is still struggling with their problem, whereas a koi swimming downstream implies that the tattooee has already overcome their difficulty. In other cases, the koi swimming downstream can represent the season of fall, and the koi swimming upstream can represent the spring." Source and further information: http://tattoos.lovetoknow.com/Koi_Fish_Tattoos 3) "The Japanese consider the Koi to be the most energetic of fishes. This is because it is constantly moving, often churning up water. In fact, some countries are trying to minimize the Koi population because of its tendency to mess up waterways by stirring up the substrate. The Koi is also able to fight the current of the water and swim upstream. This can be interpreted in two ways: 1. Being a non-conformist – Koi swimming upstream can be interpreted as showing the philosophy of non-conformism because of the fact that the Koi does not “go with the flow”. This can mean a person is very independent minded and does not do things the way they are expected of him or her. Swimming upstream can mean that a person is not easily influenced by others and does what he or she wants. 2. Strength in time of adversity – Koi fish also symbolizes persistence and the willingness to go on even though you are being swept away. It also symbolizes surpassing expectations. The Koi fish swimming upriver can show that a person has overcome various obstacles and not only does he or she keep standing, but he or she has come out victorious." Source and further information: http://www.infokoi.com/The_Meaning_of_Koi_Fish_Symbols.html