The Koi represents perseverance. Legend says a koi that swims upstream and leaps the Dragon Gate transforms into a Dragon. It symbolizes overcoming adversity to attain a higher state.
Spiritual Significance
It is a symbol of "Spiritual Ascension." The struggle against the current is what builds the spiritual muscle necessary for transformation.
Psychological Perspective
It represents "Resilience." You are swimming against the flow of collective opinion or difficulty, but you have the strength to make it.