One of the primary reasons the fish is symbolic in Japanese culture is because it is known for swimming upstream no matter what the conditions are. These fish are even said to swim up waterfalls. This is viewed as an absolute show of power because they will continue to swim upstream as if on a mission. They cannot be distracted or deterred by anything.The fish signifies freedom from all restraint. As in the water a fish moves easily in any direction, so in the Buddha-state the fully-emancipated knows no restraints or obstruction.