The koi fish 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... 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.
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.More generally, the Japanese associate koi (also known as carp) with perserverance 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.
As for the direction to where the Koi fish is facing, it is widely believed by the Japanese personalities that a Koi fish that swims down symbolizes the act of overcoming the hardships that come along the way. Meanwhile, if the Koi fish swims up, it means that the obstacles have already been overcome. (so having one in each direction would show the presence of both actions)
The Japanese recognized these fish not just for their beauty, but for their ability to transform the observer into other-worldy states of perception. These altered states of perception ultimately lead to the attraction of high energy - and this manifests in the form of prosperity of all kinds in our lives.
(I put my favorite parts in bold for effect)
Also important, I feel, is the imagery and meaning of the dragon, as the legend of the koi includes its becoming a dragon after completing its upstream battle:
The word "dragon" derives from Greek δράκων (drakōn), "a serpent of huge size, a python, a dragon" and that from the verb δέρκομαι (derkomai) "to see clearly"
In the universal language of mind the dragon represents the final stages of learning the correct use of the ego. At the beginning of our journey, we work to become aware of the conscious ego. This is where all our doubts and fears come from. The initial step is to gain control of the physical body and the conscious ego. All work is toward re-identifying with our true self or "I AM" which is the ego in it's purest form.
In Tibetan buddhism, the dragon thunders in the sky with the sound of compassion that awakens us from delusion and increases what we can know through hearing. Dragons have the power of complete communication. Just as we do not see sound, we do not see dragons.
Also important is the symbolism of the yin-yang:
The concept of yin and yang describes two opposing and, at the same time, complementary (completing) aspects of any one phenomenon (object or process) or comparison of any two phenomena.
So there. Thoughts?
