The Koi fish is pure perseverance - Koi swimming upstream can be interpreted as showing perseverance because of the fact that the Koi does not "go with the flow". This can show a person how to be strong in the face of adversity and develop strength of character or purpose. The Carp can also represents wisdom, knowledge, longevity, and loyalty.
Strength in time of adversity - Koi fish also symbolizes persistence and the willingness to go on even though it is being swept away. It also symbolizes surpassing obstacles. The Koi fish swimming upriver can show how to overcome various obstacles and how come win victory over outside influences.