Koi fishes are good luck too.

"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 (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."
From FAQ Farm.