Yes – they are Koi fish.
According to Japanese legend if a koi succeeded in climbing the falls at a point called Dragon Gate on the Yellow River it would be transformed into a dragon. Based on that legend, it became a symbol of worldly aspiration and advancement.
More generally, the Japanese associate koi with perseverance in adversity and strength of purpose. Because of its strength and determination to overcome obstacles, the koi represents courage and the ability to attain high goals.
Others say it means good fortune or luck. There are three fish to represent the three founders.
Source: Yahoo Answers